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ROCK  DRILLS 

DESIGN,    CONSTRUCTION, 
AND    USE 


BY 

EUSTACE  M.  WESTON 

Associate  School  of  Mines,  Ballarat;  Reef  Lecturer  on  Mining, 
Transvaal  University  College 


OF  THE 

UNIVERSITY 

OF 


McGRAW-HILL  BOOK  COMPANY 

239  WEST  39TH  STREET,  NEW  YORK 
6  BOUVERIE   STREET,  LONDON,  E.C. 

1910 


Copyright,  1910,  by  the  McGRAW-HiLL  BOOK  COMPANY 


GENERAL 


The  Plimpton  Press  Norwood  Mass.  U.S.A. 


PREFACE 

IN  presenting  this  collection  of  essays  on  rock  drills,  I  make 
no  claim  to  have  treated  the  subjects  exhaustively.  Rock  drills 
have  formed  the  subject  of  numerous  articles  in  the  technical 
press.  Various  authors  have  dealt  with  the  subject;  but  only 
incidentally  and  as  a  branch  of  other  subjects.  I  know  of  no 
book  that  will,  in  the  first  place,  give  a  description  of  the  leading 
modern  makes  of  English,  Australian,  and  American  drills  of 
both  piston  and  hammer  types,  or  give  such  details  of  their 
actual  use  in  metalliferous  mines  as  would  enable  a  novice  to 
approach  them  with  some  previous  knowledge;  and,  at  the  same 
time,  assist  the  engineer  and  mine  manager  to  choose  machines 
most  suited  to  his  particular  needs  and  to  maintain  and  work 
them  at  their  highest  efficiency.  This  is  my  excuse  for  attempt- 
ing such  a  task,  while  engaged  in  other  mining  work. 

I  have  not  hesitated  to  reprint  much  of  the  writing  of  others, 
always,  I  hope,  with  due  acknowledgment.  Where  the  facts  were 
stated  concisely  and  clearly  I  saw  no  object  in  transcribing.  I 
had  much  help  from  H.  P.  Gillette's  excellent  book,  C.  LeNeve 
Foster's  and  other  works  on  mining.  I  have  borrowed  largely 
from  proceedings  of  scientific  societies  and  from  A.  and  Z.  Daw's 
exhaustive  work  on  Blasting  Rock.  Many  thanks  are  due  to 
manufacturers  for  much  help.  I  have  tried  to  write  without 
bias  in  comparing  the  merits  of  various  machines  and  devices, 
and  the  book  is  not  an  advertisement  for  any  particular  drill. 

I  have  not  given  much  space  to  either  rotary  or  gasoline  drills 
as  they  scarcely  come  within  the  scope  of  the  book. 

My  apology  to  my  critics,  who  will  doubtless  find  many  omis- 
sions in  the  book,  is,  that  it  is  a  collection  of  notes  that  the  author 
himself  would  have  been  very  pleased  to  have  had  in  book  form 
when  recently  selecting  and  working  rock  drills.  My  chief 
qualification  for  writing  this  book  is,  that  I  have  had  to  earn 
my  living  by  using  many  of  the  machines  described,  and  more 
recently  in  superintending  rock-drilling  operations.  For  the 


vi  PREFACE 

scanty  and  inadequate  discussion  of  many  of  the  problems,  my 
excuse  is,  that  there  is  much,  I  believe,  not  yet  known  to  any 
one;  there  is  much  vacant  ground  for  careful  and  intelligent 
experiment  and  invention. 

Hammer  drills  are  only  now  being  developed;  designs  are 
changing  every  month;  difficulties  are  being  overcome  and  some- 
times new  ones  encountered;  nor  has  the  last  word  been  said  in 
the  design  of  piston  drills. 

E.  M.  WESTON. 

OCTOBER,  1910. 


CONTENTS 

CHAPTER  PAGE 

PREFACE      v 

I     HISTORICAL  SKETCH 1 

II    STANDARD  PISTON  DRILLS 8 

III  HAMMER  DRILLS 49 

IV  ELECTRIC  DRILLS 85 

V    OPERATING  ROCK  DRILLS  ON  THE  SURFACE  AND  UNDERGROUND  105 

VI    PISTON  DRILLS  DESIGNED  TO  USE  AIR  EXPANSIVELY     .      .      .  122 

VII     PHILOSOPHY  OF  THE  PROCESS  OF  DRILLING  ROCK    ....  129 

VIII     REPAIR  AND  MAINTENANCE  OF  ROCK  DRILLS            ....  141 

IX     DRILL  STEEL  AND  DRILL  BITS 150 

X    EXPLOSIVES  AND  THEIR  USE 178 

XI    THEORY  OF  BLASTING  WITH  HIGH  EXPLOSIVES 210 

XII     EXAMPLES  OF  ROCK  DRILL  PRACTICE,  AFRICA  AND  AUSTRALIA  226 

XIII     EXAMPLES  OF  ROCK  DRILL  PRACTICE,  AMERICA 269 

XIV     ROCK  DRILL  TESTS  AND  CONTESTS 315 

XV    DUST  AND  ITS  PREVENTION 338 

XVI     NOTES  ON  THE  USE  OF  COMPRESSED  Am       .  .     .  .351 


VII 


ROCK  DRILLS 


HISTORICAL  SKETCH 

HISTORY  has  not  handed  down  the  name  of  the  genius  who 
first  conceived  the  idea  of  drilling  a  circular  hole  in  hard  rock 
by  hammering  and  revolving  chisels  of  bronze,  iron,  or  steel, 
which  had  the  length  of  cutting  edge  decreased  as  the  depth  of 
the  hole  increased  to  provide  for  wear.  Such  holes  were  drilled 
for  building  and  bridge  work,  centuries  before  the  invention  of 
gunpowder. 

As  might  be  expected,  several  nations  contend  for  the  honor 
of  having  first  produced  a  machine  driven  by  air  or  steam  for 
boring  holes  in  hard  rock.  The  truth  is,  that,  like  most  other 
inventions,  the  rock  drill  has  been  and  is  being  gradually  per- 
fected by  the  efforts  of  different  men,  each  contributing  something 
to  the  final  design. 

Richard  Trevithick,  a  Cornishman,  invented,  in  1813,  a  rotary, 
steam-driven  drill  for  boring  in  limestone.  The  idea  of  fasten- 
ing a  detachable  tool  to  a  mechanically  moved  piston  rod  dates 
from  the  invention  of  the  steam  hammer,  about  1842.  In  1844 
Brunton,  in  England,  suggested  the  employment  of  compressed 
air.  for  a  rock  borer  and  invented  a  machine  he  called  a  "wind 
hammer,"  for  boring  holes,  as  shown  in  Fig.  1.  In  1853  William 
Pidding  invented  a  hammer  secured  to  a  frame  and  reciprocated 
by  steam  power  for  rock  boring.  In  Germany,  at  the  same 
time,  Schumann  invented  a  machine  for  work  in  the  Freiberg 
mines,  which,  in  many  features,  anticipated  the  present  type  of 
rock  drills. 

In  France,  in  1855,  M.  Fontainmoreau  patented  an  improved 
drill  for  use  with  compressed  air,  which  had  a  rotary  and  a  for- 
ward movement;  in  the  same  year  Mr.  Bartlett  patented  a  ma- 
chine tried  in  boring  the  Mt.  Cenis  tunnel;  this  drill  (Fig.  2)  was 
improved  by  M.  Sommeiller  and  used  in  boring  the  tunnel.  Two 
hundred  machines  had,  however,  to  be  kept  on  hand  in  order  to 
keep  sixteen  in  constant  use.  The  Sommeiller  machine,  a  true 

1 


2  ROCK  DRILLS 

pneumatic  percussive  drill,  was  the  first  to  be  actually  used  for 
tunnelling  (1861),  and  for  mining  at  Moresuet,  Belgium  (1863). 
Americans  claim,  and  I  think  rightly,  that  the  first  inventor 
of  a  machine  embodying  the  principles  of  the  modern  rock  drill 
was  J.  W.  Fowle,  of  Boston.  This  drill  was  steam  driven;  the 
bit  formed  an  extension  of  the  piston  rod  and  was  fed  towards 
the  rock  as  the  drill  tool  advanced.  The  piston  was  also  given 
a  slow  rotary  movement.  The  date  of  the  patent  is  1849.  A 
recent  writer  in  the  " Mining  &  Scientific  Press"  gives  the  name  of 


FIGS.  1  and  2.  —  Brunton's  "Wind  Hammer"  at  the  top,  and  M.  Sommeil- 
ler's  "Perforator"  below. 

Gen.  H.  H.  Haupt  as  being  connected  with  the  design  of  a  rock 
drill  in  1857-1861  which  was  of  better  design  than  those  at  work 
in  the  Mt.  Cenis  tunnel.  It  was  improved  by  Taylor,  and  did 
best  work  in  driving  the  St.  Gothard  tunnel.  This  drill  was  im- 
proved by  Burleigh,  who  constructed  a  tunnel-drilling  machine 
which  was  used  in  driving  the  Hoosac  tunnel  in  Massachusetts, 
in  1866.  Other  names  associated  with  the  development  of  the 
rock  drill  are  Crease,  Jordan,  Darlington,  Beaumont,  Doering, 
Ingersoll,  Sergeant,  Wood,  Leyner,  Holman,  Stephens,  and  others. 
Fig.  3  shows  the  type  of  drill  used  in  1880. 


HISTORICAL  SKETCH  3 

The  history  of  the  rock  drill  written  from  another  standpoint 
could  be  called  the  history  of  modern  mining  and  of  much  modern 
engineering.  It  is  not  too  much  to  say  that  without  the  rock 
drill  the  world  would  long  before  this  have  starved  for  its  indus- 
trial and  precious  metals.  The  rock  drill  has  added  enormously 
to  the  wealth  of  the  world.  Mines,  some  of  them  the  richest, 


FIG.  3.  —  A  rock  drill  of  1880. 

and  quarries  in  hard  rock,  where  labor  was  scarce  and  dear,  have 
been  rendered  workable  only  by  its  use.  The  world's  greed  for 
gold,  silver,  lead,  copper,  and  tin  could  never  have  been  satis- 
fied without  it.  The  wonderful  mining  undertakings  of  the  past, 
the  great  drainage  adits  of  Saxony  and  Cornwall,  the  deep  shafts 
and  drives  in  hard  ground  in  these  old  mines  were  accomplished 
only  by  the  expenditure  of  an  amount  of  time  and  human  effort 


4  ROCK  DRILLS 

that  we  cannot  afford  in  these  clays  of  large  demands  and  large 
outputs.  The  rock  drill  with  its  hundreds  of  crushing  blows  per 
minute,  doing  the  work  of  ten  or  twenty  men,  came  to  help  the 
miner  extract  bodies  of  low-grade  ore;  to  enable  the  engineer  to 
attack  problems  undreamed  of  before;  and  in  the  Old  World  to 
pierce  the  Alps  for  his  railways  by  the  Mt.  Cenis  tunnel  1\  miles 
long;  the  St.  Gothard  tunnel  9J  miles  long,  and  the  Simplon 
tunnel  12  miles  long.  In  the  New  World  great  aqueducts,  like 
the  Croton,  could  be  carried  by  tunneling  for  34  miles,  and  every- 
where the  great  railroads  were  carried  through  the  heart  of  the 
Alleghanies  and  Rockies  as  surely  as  over  the  Mississippi  plains. 
In  the  Chicago  drainage  canal,  14  million  cubic  yards  of  solid 
rock  were  removed  in  an  incredibly  short  space  of  time  by  their 
aid;  and,  finally,  the  great  continents  of  North  and  South  America 
are  being  rent  asunder  by  the  greatest  cut  in  solid  rock  ever  made 
by  man  and  only  possible  by  the  aid  of  the  percussive  rock  drill. 
Everywhere,  canals,  tunnels,  railroads,  docks,  harbors,  and 
numerous  other  works  have  been  made  possible,  as  commercial 
undertakings,  largely  by  the  rock  drill.  Twenty  to  thirty  thou- 
sand rock  drills  are  at  work  in  the  world  to-day.  There  are  about 
2500  employed  in  the  Witwatersrand  field  in  South  Africa.  With- 
out their  aid  in  stoping  and  development,  the  output  of  nearly 
2J  millions  pounds  sterling,  per  month,  could  not  be  maintained; 
financial  disaster  would  hover  over  the  whole  civilized  world, 
owing  to  a  shortage  of  gold. 

Cheap  roads,  paving,  and  building,  cheap  rail  travel  and  trans- 
portation and  low-priced  metals,  we  owe  largely  to  the  rock  drills, 
and  even  in  death  the  rock  drill  helps  to  provide  our  graves  with 
head  stones.  This  might  remind  us  that  the  history  of  the  rock 
drill  has  something  of  tragedy  and  terror  connected  with  it.  In 
many  mining  fields  the  standard  percussive  rock  drill  is  not 
operated  without  the  cost  of  valuable  human  lives.  In  the  first 
place;  its  use  permits  so  many  blasts  that  the  air  in  the  mine 
workings  is  burdened  with  a  greatly  increased  proportion  of  the 
products  of  the  combustion  of  high  explosives.  Of  these  carbon 
monoxide  and  nitrous  acid  are  -active  poisons  rapidly  producing 
death  when  present  in  large  quantities;  these  gradually  sap  the 
strength  and  vitality  when  breathed  during  long  periods,  even 
when  present  in  very  small  amounts.  Adequate  ventilation  may 
deal  with  this  trouble.  The  rock  drill  when  engaged  in  drilling 


HISTORICAL  SKETCH  5 

holes  pointed  upward  produces  its  cuttings  in  the  form  of  fine 
dust.  This  dust  when  inhaled  by  the  miner  remains  on  the 
lungs,  choking  and  weakening  the  tissues  and  after  a  time  pro- 
duces a  painful  death.  The  life  of  a  rock  driller,  engaged  in 
development  work  on  the  Rand  field  in  South  Africa,  owing  to 
these  two  causes,  has  been  stated  to  average  not  more  than  five 
years.  This  subject  will  be  referred  to  later  in  discussing  the 
problem  of  boring  with  hollow  steel  water  jets  and  sprays. 

The  following  interesting  chronological  table  is  taken  with 
the  preceding  figures  from  Messrs.  Holman  Brothers'  catalogue. 


CHRONOLOGICAL  TABLE 

AN  interesting  compilation  of  some  of  the  most  important  events  concerning 
rock  drills,  boring  shot  holes,  explosives,  and  blasting  ground.  Partly  com- 
piled by  Eziha  and  Drinker  and  supplemented  with  additional  information. 
From  Transactions  P.  S.,  Vol.  14. 

A.D. 

1280  Albert  Magnus,  the  German  Friar,  describes  an  explosive  powder. 

1284  Roger  Bacon  notices  the  composition  of  an  explosive  powder. 

1324  Berthold  Schwarz  is  said  to  have  invented  gunpowder. 

1412  Gunpowder  manufactured  in  England. 

1613  Martin  Weigel,  mining  superintendent  of  Freiberg,  proposed  drilling 

and  blasting  in  mines. 

1670  German  miners  introduced  blasting  into  England. 

1685  Tamping  with  clay  known  in  Saxony. 

1687  Lumbe  introduced  into  the  Harz,  tamping  with  clay,  and  straws  filled 

with  powder  for  firing  the  shot  holes. 

1688  Singer,  of  Clausthal,  employed  small  firing  tubes  of  hard  wood. 

1689  Luft,  of  Clausthal,  used  paste  board  cartridges. 

1717     Fritsch  proposed  to  save  powder,  and  to  break  the  rock  by  wedges 

driven  into  the  bore  holes. 
1725     At  this  date  the  effect  of  simultaneous  firing  of  several  shots  was 

known. 
1749     Hungarian  miners  first  introduced  the  chisel-bit  drill  into  the  Harz. 

For  a  period  of  one  hundred  and  thirty-six  years,  from  WeigePs  day 

to  this  date,  all  drilling  had  been  done  by  means  of  crown  and  cone 

"bits." 

1759  Drilling  with  a  chisel  bit  introduced  into  Saxony. 

1760  Thumberg  introduced  into  Sweden  tamping  with  wedges. 
1791     Le  Plat  used  sand  as  a  tamping. 

1795     Humboldt  proposed  making  the  shot  holes  wider  at  the  bottom  (of  a 

conical  shape). 
1811     Spangenberg,  of  Sahl,  used  wooden  tamping  rods,  also  wooden  needles 

and  soft  clay  for  tamping. 


6  ROCK  DRILLS 

1813  Trevithick  invented  a  rotating  boring  machine,  which  was  made  at 
Hayle  Foundry,  Cornwall,  and  put  into  operation  at  some  limestone 
quarries  near  Plymouth. 

1823     Harris  fired  a  blast  by  the  electric  spark. 

1829  Needles  made  of  a  composition  of  lead  and  tin,  used  in  the  district  of 
Ehrenfridersdorf. 

1829  Moses  Shaw,  of  New  York,  fired  several  charges  of  powder  simultane- 
ously by  passing  an  electric  spark  through  a  priming  composed  of 
the  fulminiate  of  silver. 

1831     Bickford,  of  Camborne,  invented  the  safety  fuse. 

1834     Pischal  proposed  ignition  of  blasting  powder  by  means  of  percussion. 

1838  Prideaux  used  oxyhydrogen  for  deepening  bore  holes,  and  with  it 
burnt  a  hole  at  the  rate  of  i  of  an  inch  per  minute. 

1839  Hague  injected  water  into  air-compressing  cylinders. 

1840  Bore  holes  made  with  rotary  drills  at  Lankowily. 
1840     Cast  steel  borer  used  in  the  Derbyshire  mines. 

1844  Brunton,  of  Cornwall,  proposed  using  compressed  air  for  working  drill 

hammers,  the  air  after  use  to  improve  ventilation. 

1845  Cast  steel  drills  tested  at  Freiberg. 

1846  Schonbein  exhibited  a  sample  of  gun  cotton  at  the  British  Association 

1847  Sobrero  discovered  nitroglycerine. 

1849  Randolph  of  Glasgow,  introduced  into  an  air  compressor  a  spray  of 
water  for  cooling  the  air  during  its  compression. 

1849  Couch,  of  Philadelphia,  patented  a  "lance"  percussion  drill. 

1850  Robert  Hunt,  E.R.S.,  made  low-tension  electric  fuses  and  used  them 

in  sinking  a  pit  of  the  Abercarn  Colliery,  South  Wales,  the  firing 
of  the  fuses  having  been  performed  by  means  of  an  electric  battery. 
The  holes  were  bored  in  one  operation,  and  fired  simultaneously  in 
volleys.  The  holes  were  placed  so  as  to  obtain  a  "sink"  of  ground 
from  the  blast. 

1851  Fowle,  of  Philadelphia,  patented  a  direct  action  percussion  drill. 
1851     Cav6,  of  Paris,  invented  a  reciprocating  percussion  drill. 

1853  Piatti  proposed  using  compressed  air  in  the  construction  of  the  Mont 

Cenis  Tunnel. 

1854  Bartlett's  rock  drill  tried  at  the  Mont  Cenis  Tunnel. 
1854     Schumann  invented  his  percussion  power  drill. 
1857     Schumann's  drill  employed  in  the  Freiberg  Mines. 

1857     Sommeiller  invented  a  drill  for  use  in  the  Mont  Cenis  Tunnel. 
1857     Ebner  employed  a  frictional  machine  for  blasting. 
1857     Schwarnzkopf's  drill  tried  at  Bingen. 

1861  On  the  1st  of  January,  Sommeiller's  perfected  drill  commenced  to 
work  at  the  Mont  Cenis  Tunnel. 

1861  Lisbet   applied   his    boring  machine   in    soft   rock    (coal,  soft   lime- 

stone, etc.) 

1862  Bornhardt's  air-tight  electric  firing  machine  brought  into  successful  use. 

1863  Edward  Crease  introduced  his  rock-boring  machine  into  the  Clogan 

Mines,  North  Wales. 
1863     Lowe  rock  drill  invented. 


HISTORICAL  SKETCH  7 

1863     Sach's  rock  drill  invented. 

1863  Noble  applied  nitroglycerine  as  a  blasting  agent. 

1864  In  March,  Carl  Sach's  machine  introduced  in  the  Altenberg  Mines, 

Aix-la-Chapelle. 

1865  Gun  cotton  tried  at  Hoosac  Tunnel. 

1866  Lithofracture,  manufactured  by  Ergels,  near  Cologne. 

1866     Nitroglycerine  tried  with  great  success  in  the  Hoosac  Tunnel. 
1866     Jordan  and  Darlington  invented  the  rifle-bar  and  ratchet  wheel  for 
turning  the  piston  carrying  the  drill. 

1866  The  Burleigh  drill  successfully  introduced  at  the  Hoosac  Tunnel. 

1867  Jordan  and  Darlington  invented  the  straight  and  spiral  shot,  and  double 

ratchet  wheel  for  turning  the  drill. 
1867     Dynamite  patented  in  England. 

1867     Doering  introduced  his  boring  machine  into  the  Tincroft  Mines. 
1867     Dubois  and  Francois  rock  drill  invented. 
1870     Beaumont  and  Appleby's  diamond  boring  machinery  introduced  at 

the  Croesor  United  Slate  Quarries,  North  Wales. 
1870     Sir  George  Denys,  Bart,  commenced  driving  an  adit  for  the  Old  Gang 

Company,  Yorkshire,  by  means  of  the  McKean  drills. 
1873     The  Ferroux  rock  drill  invented. 

1873  The  Darlington  rock  drill  invented. 

1874  The  Mowbray  mica  powder  patented. 

1874    Electric  blasting  introduced  by  Darlington  into  the  Minerva  Mines; 

Bonhardt's   machines,   the  blasting  stick,   and   wire  electric  fuses 

being  employed  for  that  purpose. 
1874     Darlington  invented  the  spinning  piston. 
1876     The  Beaumont  rock  drill  employed  at  Carn  Brea. 
1879     Rock  drills  made  at  the  Camborne  Engineering  Works. 
1904     The  world's  record  for  Incline  Shaft  Sinking  by  the  Holman  drill, 

S.  Africa. 


II 

THE  STANDARD  PISTON  DRILL 

THE  standard  drill  consists  essentially  of  a  piston  to  which 
is  attached  a  cutting  tool.  This  piston  reciprocates  within  a 
cylinder,  and  its  movement  is  usually  governed  by  a  valve.  The 
rear  end  of  the  cylinder  contains  a  ratchet  wheel,  pawls,  and  rifle 
bar  to  rotate  the  piston  and  boring  tool.  The  cylinder  is  mounted 
on  a  cradle  in  such  a  manner  that  it  may  be  fed  forward  towards 
the  rock;  the  cradle  is  attached  by  its  seat  to  some  rigid  support. 

PRINCIPAL  PARTS  OF  STANDARD  DRILL 

Fig.  4  shows  the  more  important  portions  of  a  well-known 
drill:  1,  handle;  2,  crosshead  held  by  standards  from  the  cradle 


FIG  4.  —  Section  of  Sergeant  drill,  showing  principal  parts. 

not  shown;  3,  box  on  cylinder  with  its  lines  and  lock  nuts;  4,  feed 
screw  to  move  cylinder  forward;  5,  nuts  on  end  of  side  rod;  6,  buffer 
plate;  7,  ratchet  pawls  and  release  ring;  8,  rifle  bar;  9,  piston  with 
packing  ring  18;  10,  cylinder;  11,  auxiliary  valve;  12,  main  piston 
air  valve;  13,  valve  chest;  14,  cradle  with  guides  and  seat;  15,  front 
head  with  packing  (this  is  not  of  most  recent  design);  16,  clutch 
or  tool  holder,  with  U-bolt;  21,  22,  pad  or  key;  19,  packing;  20, 
removable  bushing;  17,  air  port  in  cylinder. 

The  accompanying  Table  I  shows  the  sizes  generally  supplied 
by  all  makers  of  most  standard  machines.  This  example  is 
taken  from  the  Ingersoll-Rand  Company's  catalogue: 


STANDARD   PISTON   DRILL 


a  § 


io"§XotH-w    2°t2°t2®co3coo 


CO  '"'O       PH 

^  nlao^J1         O 


T3y 

"'"*  .-th*1  ,__,  O 


^  *«,H         QO 


Jr-llO'-HOO 


,H  .,-(1-1          GO 


00   0 


T-II-1          rl  1-H  .-H  T}<  W 


c          c 


,2  g     ^  g  c    ;    :  fl 


yiiniiH  1] 

:^a  :§  :  :  :Ss  !      :  : 

ft     ."     >   »  -  .     «  w  3 

'^t^-i         ]      03          .         [          IQQ'MO)  ^ 


M 


2  cS     .5.5    •   • 


, 


'^-rt       a; 


x3^GS2rr—  °3'«iu*J 


I 

fcfc^^o 


:*J 

J| 

. «  r 

ill 
;-ss 


«.»   •  o 
I1    ;5 

^^^^^^iP 


;3|iiSi!PliiiiMiiJ|il 

I^P^sIll.a^|^ffiM^IS 


fsiUJUlplf^o 

M»JQ*tS 


10  ROCK  DRILLS 

CLASSIFICATION  OF  PISTON  DRILLS 

Piston  rock  drills  may  be  divided,  first,  into  two  main  divisions: 

(1)  Those  in  which  the  movement  of  the  operating  fluid  is 
controlled  by  a  separate  valve  or  valves,  and  (2),  those  in  which 
the  piston  itself  acts  as  a  valve. 

Valve-operated  machines  may  be  divided  into  four  main 
classes : 

(a)  Tappet  valve  machines,  in  which  the  movements  of  the 
piston  control  those  of  the  valve  through  a  positive  mechanical 
connection. 

(6)  Air  valve  machines,  in  which  the  motions  of  the  piston 
control  that  of  the  valve  by  varying  air  pressures  on  the  valve 
surfaces,  transmitted  through  suitable  direct  passages  in  the 
walls  of  the  cylinder. 

(c)  Corliss  valve  machines,  in  which  a  Corliss  valve  or  valves 
is  operated  by  tappets  and  levers,  or  by  fluid  pressure. 

(d)  Auxiliary  valve   machines.     In  these   machines  the  dis- 
tribution of  the  operating  fluid  to  reverse  the  valve  is  controlled 
by  a  valve,  or  valves,  which  is  itself  positively  controlled  by  the 
movements  of  the  piston. 

Piston  Valve  Drills 

The  piston  machines,  or  those  of  the  second  division  above 
mentioned,  have  practically  become  obsolete,  though  attempts 
are  now  being  made  to  modify  them  for  use  as  small  st oping  drills. 
In  South  Africa  a  small  stoping  drill  of  the  Konomax  type  is  being 
experimented  with,  built  on  this  principle  with  devices  designed 
to  overcome  previous  defects.  The  Adelaide,  Darlington,  and 
Minerva  drills  were  of  this  type. 

In  the  Darlington  drill,1  compressed  air  always  acts  through 
the  port  p,  Fig.  5,  in  the  annular  space  o  on  the  front  of 
piston,  and  drives  it  back  until  the  passage  n  is  opened,  which 
allows  the  air  to  act  on  the  larger  surface  on  the  back  of  pis- 
ton b.  This  drives  it  forward  until  the  exhaust  port  e  is  un- 
covered when  the  cycle  is  repeated.  From  the  figure  it  will  be 
seen  that  that  portion  of  the  stroke  from  e  to  m  is  produced  by 
expansion. 

1  Holman  Bros.  Catalogues. 


STANDARD   PISTON   DRILL 


11 


The  Adelaide  drill,1  Fig.  6,  "was  preceded  in  time  by  the 
Darlington  drill,  of  which  it  may  be  regarded  as  a  modification. 
A  A  represent  the  annular  port,  admitting  the  air  all  round  the 
piston,  and  BI  BI  are  ports  in  the  piston-rod.  When  the  latter 
are  opposite  A  A,  air  passes  down  through  the  space  C  in  the 
piston-rod  to  the  rear  end  of  the  piston,  and  drives  it  forward 


FIG.  5.  —  Darlington  sloping  drill. 

till  it  uncovers  the  port  B,  which  puts  this  part  of  the  cylinder 
into  communication  with  the  atmosphere.  At  the  same  time 
#1  BI  have  passed  beyond  the  stuffing-box  and  part  of  the  exhaust 
escapes  in  that  direction;  while  this  is  happening  the  long  shallow 
annular  recess  cut  in  the  piston-rod  is  brought  to  A,  the  air  presses 
on  the  small  annular  space  at  the  front  end  of  the  piston  and 


FIG.  6.  —  Adelaide  drill,  showing  principal  parts. 

drives  it  back.  It  will  be  noticed  that  this  drill  uses  the  air 
expansively,  for  when  once  BI  has  gone  past  A  no  further  supply 
of  power  is  taken  in.  D  is  the  rifled  bar,  E  the  ratchet  wheel, 
H  the  feed-screw,  and  G  the  feed-nut,  similar  to  the  correspond- 
ing parts  of  many  other  machines." 

Advantages  and  Disadvantages.  —  There  is  no  separate  valve 
or  valve  chest  required;  the  weight  can  be  reduced  and  there  are 
1  C.  Le  Neve  Foster's  Text  Book  of  Ore  and  Stone  Mining. 


12  ROCK  DRILLS 

fewer  moving  parts.  They  use  air  expansively.  The  disadvan- 
tages outweigh  any  advantages.  The  blow  struck  is  generally 
cushioned,  thus  reducing  their  cutting  efficiency,  and  they  are 
not  as  rapid  drillers  as  are  valve  machines.  The  piston  is  often 
weakened  by  having  ports  cut  in  it,  and  owing  to  the  small, 
effective  annular  area,  the  return  stroke  is  not  powerful.  Hence 
in  holes  offering  side  friction,  or  in  drilling  deep  holes,  it  gives 
trouble.  Another  disadvantage  is  that  in  actual  work,  once  the 
cylinder  begins  to  wear,  the  air  leaks,  both  ways  past  the  piston, 
thus  increasing  the  air  consumption. 

Tappet  Valve  Drills 

Tappet  valve  drills  were  the  earliest  design  made  for  regular 
work,  and  are  now  the  only  type  really  suitable  for  work  with 
steam,  as  the  condensation  of  the  steam  interferes  with  other 
valve  actions.  They  have  also  special  advantages  for  certain 
work  which  have  prevented  them  becoming  obsolete.  The  valve 
motion  is  positive  and  not  affected  by  moisture  in  compressed 
air.  The  machine  will  keep  on  boring  a  hole  that  may  offer  great 
frictional  resistance,  where  some  other  drills  would  stick. 

Disadvantages.  —  These  drills  cannot  deliver  a  perfectly  "free" 
or  "dead"  blow.  In  other  words,  there  is  always  some  exhaust 
air  from  the  front  of  the  piston,  caught  between  it  and  the  cylinder 
by  the  reversal  of  the  valve  just  before  the  forward  stroke  is 
finished.  In  some  ground  this  is  by  no  means  a  defect,  for  where 
the  ground  is  dead  or  sticky  this  cushion  helps  to  "pick  the  drill 
up"  for  a  rapid  and  sure  return  stroke,  preventing  its  sticking 
and  insuring  a  maximum  number  of  blows  per  minute.  The 
length  of  stroke  must  be  kept  long  enough  for  the  movement  of 
the  piston  to  knock  over  the  valve.  The  valve  on  the  Rio  Tin  to 
machine  is  a  piston,  or  spool  valve;  on  other  machines  the 
valve  is  of  the  plain  D-slide  valve  type.  The  Rand  "giant" 
drill  has  a  device  to  reduce  the  total  air  pressure  on  the  back  of 
valve;  but  most  of  the  others  have  the  full  pressure  of  steam  or 
air  on  the  back  of  valve.  This  of  course  makes  the  valve  take 
up  its^own  wear  and  form  its  own  bearing  surface,  thus  reducing 
leakage.  The  seats  generally  require  periodical  cleaning  and  are 
raised  to  give  material  to  allow  "scraping  up." 

Where  the  lubrication  is  deficient,  as  it  generally  is,  the  coeffi- 


STANDARD   PISTON   DRILL  13 

cient  of  friction  may  reach  25  per  cent.,  especially  in  the  presence 
of  grit.  Taking  a  valve  area  of  6  sq.  in.  exposed  to  80-lb.  pres- 
sure, it  might  require  a  force  of  120  Ibs.  to  move  the  valve.  This 
means  that  the  blow  struck  by  the  piston  is  retarded  to  a  corre- 
sponding degree,  and  in  some  makes  the  valve  tends  to  wear  its 
seat  into  an  irregular  surface.  Some  writers  have  contended 
that  the  turning  movement  of  the  piston  is  also  hindered;  but 
as  the  blow  of  the  tappet  occurs  at  the  beginning  and  end  of  the 
stroke,  while  the  turning  movement  is  a  positive  and  continuous 
one  along  all  the  length  of  the  back  stroke,  this  effect  is  not  notice- 
able. As  the  tappet  is  struck  400  to  600  times  per  minute,  the 
wear  and  stress  is  great.  Specially  hardened  surfaces  on  pistons 
and  tappets  are  needed  as  well  as  large  wearing  surfaces,  or  renew- 
able bushings,  for  the  tappet  to  rock  on.  When  wear  takes  place 
the  throw  of  the  valve  is  reduced;  cushioning  becomes  greater 
and  the  stroke  is  shortened.  The  resistance  and  pressure  of  the 
tappet  tends  to  throw  increased  and  unequal  wear  on  the  oppo- 
site side  of  the  cylinder. 

The  drills  described  in  the  following  pages  are  those  made  in 
America  by  the  Ingersoll-Rand  Company;  the  Sullivan  Machinery 
Company,  and  the  Chicago  Pneumatic  Tool  Company.  The 
English  examples  are  the  Holman  drill,  Stephens  Climax  drill, 
and  the  Rio  Tinto  drill. 

Ingersoll-Rand  Drill.  —  Regarding  the  design  of  the  "Arc 
Valve"  tappet  drill,  the  makers  state  that  it  "is  an  evolution  from 
earlier  patterns  in  which  the  defects  of  the  pioneer  models  are 
corrected.  It  is  distinguished  from  other  tappet  types  by  its 
arc-shaped  valve,  moved  on  a  circular  seat  by  a  rocking  tappet, 
all  concentric  with  the  rocker  pin." 

Rand  "Little  Giant"  —  The  following  description  of  the 
Rand  "Little  Giant"  rock  drill,  Fig.  7,  is  taken  from  the  maker's 
catalogue. 

"The  valve  mechanism  is  made  up  of  three  pieces,  the  valve, 
the  rocker,  and  the  rocker  pin.  The  rocker,  turning  on  the  rocker 
pin,  is  in  contact  with  the  piston  at  one  point  and  projects  into 
the  valve  in  its  upper  arm,  which  ends  in  a  globular  form.  When 
the  piston  moves,  a  curved  surface  slides  under  a  rocker  contact, 
pushing  the  rocker  upward  and  swinging  the  valve  in  the  same 
direction  as  the  piston  moves.  On  the  reverse  travel  of  the 
piston,  this  series  of  movements  is  exactly  reversed.  An  exam- 


14 


ROCK   DRILLS 


ination  of  the  sectional  view  of  the  Little  Giant  reveals  the  follow- 
ing important  facts: 

(a)  "The  piston  does  not  strike  the  rocker.  It  simply  slides 
under  it  gently  and  pushes  it  up.  The  curve  of  the  contact  sur- 
face of  the  piston  is  such  that  the. movement  is  the  easiest  possible, 
and  the  line  of  action,  instead  of  being  through  or  against  the 
rocker  pin,  is  such  that  the  effort  is  transmitted  directly  to  the 
point  of  contact  between  rocker  ball  and  valve.  There  is  thus 
no  hammering  action,  no  tendency  to  bind  or  cut  on  the  rocker 
pin.  The  latter  is  simply  a  free  support  for  the  rocker,  not  a 
thrust  bearing  opposed  to  a  hammer  blow.  This  improved  design 
gives  the  easiest  and  most  free  movement  possible  in  all  parts, 
with  the  lightest  possible  service  on  rocker,  valve,  pin,  and  piston, 
and  with  the  least  possible  reduction  of  the  force  of  the  piston 
blow. 


FIG.  7.  —  Section  of  "Little  Giant"  drill.     (Rand.) 

(b)  "The  rocker  is  symmetrical  about  its  vertical  axis  through 
rocker  pin  and  ball.     It  is  therefore  reversible,  and  cannot  be 
put  in  place  'wrong  end   to'  by  an  inexperienced  man.     This 
is  a  refinement  which  will  be  appreciated  by  those  who  have  had 
disastrous  experiences  with  non-reversible  rockers.     It  permits 
also  the  use  of  a  straight  rocker  pin,  instead  of  a  taper.     The 
holes  in  the  cylinder  for  the  rocker  pin  are  lined  with  steel  bush- 
ings which  may  be  renewed  when  worn,  and  which  work  under 
exhaust  pressure  only.     The   curves   at  either  shoulder  of  the 
piston  are  not  identical,  but  so  designed  as  to  give  the  correct 
distinction  between  forward  and  return  stroke. 

(c)  "The  arrangement  of  parts  in  their  mutual  relations  and 
in  relation  to  the  valve  is  such  as  to  secure  a  clean,  sharp  cut-off 

—  a  powerful  factor  in  air  economy. 

(d)  "The  valve  is  held  to  its  seat  by  live  pressure  on  its  upper 
face  and  thus  only  wears  tighter  with  continued  service.     The 


STANDARD   PISTON   DRILL 


15 


rocker  rests  in  a  chamber  which  is  open  to  the  drill  exhaust. 
Pressure  cannot  enter  the*  cylinder  except  through  the  ports  and 
there  can  be  no  leakage  loss  from  this  cause.  If,  when  the  piston 
rings  or  cylinder  bore  are  worn,  there  is  a  leakage  of  pressure 
past  the  piston,  this  live  pressure  passes  directly  out  through  the 
exhaust  and  cannot  retard  the  action  of  the  piston  or  reduce  the 
blow,  as  would  be  the  case  if  the  ports  were  the  exit  passages 
used.  Full  stroke  and  full  power  are  thus  maintained  under 
long  service. 

(e)  "This  valve  movement  permits  the  correct  variation  in 
admission  on  the  forward  and  back  strokes,  thus  economizing 
steam  or  air.  At  the  same  time,  the  back  stroke  is  quick  and 


FIG.  8.  —  Rand  Model  5  shell  and  cylinder  guides. 

positive,  giving  this  drill  great  power  in  ejecting  broken  frag- 
ments and  to  this  extent  improving  its  cutting  capacity. 

(/)  "The  arrangement  of  ports  and  the  travel  of  the  valve  is 
such  that  there  is  a  very  slight  cushion  on  the  forward  stroke  — 
merely  enough  to  add  life  and  speed  to  the  blow,  without  notice- 
ably reducing  its  force.  On  the  back  stroke  there  is  an  ample 
cushion  of  exhaust  steam  or  air  which,  expanding,  assists  in  the 
forward  stroke." 

Rand  Model  No.  5.  —  A  radical  change  has  been  made  in  the 
form  of  the  shell  guides,  and  the  design  used  on  the  Model  5 
drill,  Fig.  8,  is  the  V  shape  of  unusually  large  section,  providing 
ample  wearing  surfaces  for  any  position  in  which  the  drill  may 
be  worked.  The  construction  is  such  that  the  slides  will  stay  in 
the  adjustment  given  them,  for  they  cannot  slip  when  bolted 


16  ROCK  DRILLS 

down  to  the  sharp  angles  of  the  guides.  New  shells  are  fitted  with 
several  tin  liners  (at  the  point  designated  in  the  cut),  and  by  the 
removal  of  one  of  these  liners  both  top  and  side  wear  can  be  taken 
up.  These  liners  are  held  in  place  by  dowel  pins,  making  it 
impossible  for  them  to  be  displaced. 

The  Kid  and  No.  0  drills,  with  the  view  of  maintaining  light 
weight,  are  made  with  solid  shells,  and  do  not  have  adjustable 
slides,  although  fitted  with  the  V-shaped  guides.  The  shells 
are  made  of  malleable  iron,  and  can  be  closed  in  by  a  hammer 
when  wear  takes  place. 

Chicago  Giant  Rock  Drill  — "The  Chicago  Giant  rock  drill,1 


FIG.  9.  —  Chicago  Giant  rock  drill  unmounted. 

Figs.  9  and  10,  manufactured  by  the  Chicago  Pneumatic  Tool 
Company,  has  a  shell  of  the  adjustable  type,  constructed  so  as 
to  provide  for  double  side  bearing  for  the  cylinder.  The  shoe 
caps  are  made  to  take  up  wear  in  two  directions  with  one  adjust- 
ment. A  removable  cylinder  stop  is  also  provided  in  the  lower 
end  of  the  shell,  to  prevent  the  cylinder  from  slipping  out  in  case 
the  feed  screw  should  be  run  out  of  the  feed  nut.  To  remove 
the  cylinder  from  the  shell,  all  that  is  necessary  is  to  remove  the 
stop  first,  then  by  turning  the  feed  screw  to  run  the  cylinder 
down  in  until  the  feed  screw  is  out  of  the  feed  nut.  This  allows 
the  cylinder  to  be  slipped  out  of  the  shell  without  dismantling 
the  machine. 

1  Engineering  and  Mining  Journal,  April  6,  1907. 


STANDARD   PISTON   DRILL 


17 


"The  cylinder  is  cast  from  a  special  mixture,  having  a  tensile 
strength  of  35,000  to  38,000  Ibs.  The  upper  end  is  extended  to 
form  a  chamber  for  the  rotating  mechanism,  which  is  of  the  releas- 
ing type.  Three  parts  are  used,  and  the  pawls  are  reversible. 
The  ratchet  is  of  one  piece  with  the  rotating  or  rifle  bar,  which 
is  extended  on  its  upper  end  to  fit  into  a  chamber  or  recess  into 
the  upper  head;  this  provides  for  holding  the  rotating  bar  in  a 
central  position  and  relieves  the  rotating  mechanism  of  side  strains. 


FIG.  10.  —Chicago  Giant  rock  drill,  mounted. 

"The  valve  motion  is  positive  and  is  of  the  tappet  or  rocker 
type,  modified  to  give  a  short  stroke,  the  length  of  the  stroke 
being  at  all  times  under  the  control  of  the  operator.  The  sup- 
porting pin  of  the  rocker  works  in  renewable  steel  bushings  and 
is  completely  enclosed,  it  being  kept  in  place  by  caps  easily  remov- 
able but  securely  locked  in  place  by  the  valve  seat. 

"An  oil-reservoir  chamber  is  provided  in  the  valve  seat  and 
communication  is  made  between  the  oil  reservoir  and  the  interior 
of  the  valve  chest.  The  oil  is  led  through  this  channel  into  the 


18  ROCK  DRILLS 

chest  where  it  mixes  with  the  operating  fluid  and  is  carried  by 
it  into  the  interior  of  the  machine.  One  filling  of  the  oil  reservoir 
lasts  half  a  shift.  In  case  the  rotating  mechanism  should  not 
receive  sufficient  lubrication  from  the  interior,  provision  is  made 
in  the  upper  head  for  oiling. 

"The  drill  does  its  best  and  most  economical  work  when 
operated  by  compressed  air,  but  it  is  also  a  satisfactory  machine 
when  operated  by  steam." 

The  Sullivan  Tappet  Valve  Rock  Drill.  —  The  makers  state 
that  the  tappet  valve  motion  possesses  advantages  for  rock  drill- 
ing of  certain  kinds,  and  to  meet  the  demand  for  a  drill  contain- 
ing this  feature  the  Sullivan  design,  shown  in  the  accompanying 
illustrations,  is  presented.  All  details  have  been  tested  by  long 


FIG.  11.  —  Section  of  Sullivan  tappet  valve  drill  showing  the  relative  posi- 
tion of  the  working  parts. 

use,  and  its  performance,  as  to  speed,  power  economy,  and  dura- 
bility, is  most  satisfactory. 

This  drill  is  similar  in  all  respects,  except  the  valve  motion, 
to  the  Sullivan  differential  valve  machine.  This  valve  motion, 
as  will  be  seen  from  the  sectional  view,  Fig  11,  consists  of  a 
curved  rocker,  whose  ends  rest  on  beveled  surfaces  at  each  end 
of  the  piston.  These  surfaces  impart  a  circular  movement  to 
the  rocker,  causing  the  projection  at  its  center  to  operate  a  flat 
valve,  shaped  like  a  double  "D,"  which  controls  the  admission 
of  air  to  the  drill  cylinder.  Fig.  12  shows  this  drill  mounted  on 
a  tripod.  The  makers  recommend  this  drill  for  conditions  of 
low  air  pressures  and  soft  rock. 

The  severe  duty  imposed  upon  the  rocker  of  a  tappet  rock 
drill,  and  the  necessity  for  continuous  and  exact  performance 
of  its  functions,  have  made  this  part  the  subject  of  much  study. 


STANDARD  PISTON   DRILL 


19 


FIG.  12.  —  Sullivan  tappet  valve  drill  on  tripod. 


20 


ROCK  DRILLS 


STANDARD  PISTON   DRILL  21 

The  Sullivan  rocker  is  perfect  in  its  action,  cannot  be  broken, 
and  will  wear  for  years.  It  is  shaped  like  a  gear  segment,  the 
projection  at  the  top  corresponding  to  a  tooth  of  standard  rack 
form.  The  curved  ends  of  the  rocker  are  so  shaped  as  to  present 
an  ample  rubbing  surface  to  the  piston,  while  the  gear  tooth 
projection,  with  its  broad  area,  engaging  the  flat  valve,  is  a  note- 
worthy improvement  over  the  axial  pin  and  knob  used  for  this 
purpose  in  some  drills. 

The  rocker  is  of  tool  steel,  accurately  formed  and  tempered 
to  the  proper  hardness.  The  cylinder  and  valve  seat  form  a 
housing,  allowing  the  rocker  free  motion,  without  side  or  vertical 
play.  The  sloping  surfaces  of  the  piston  are  hardened,  by  an 
improved  process,  to  reduce  wear.  The  valve  is  of  close-grained 
iron,  finished  to  a  perfect  bearing  upon  the  valve  seat.  The 
latter  is  removable,  and  scraped  to  fit  the  cylinder  and  chest 
cover  without  the  use  of  gaskets.  The  cover  is  flat,  occupying 
the  least  possible  space. 

Taylor  Horsfield's  Drill  — The  New  Type  " National"  is  a 
tappet  drill  of  somewhat  novel  design.  The  pin  20,  Fig.  13,  of 
the  flat  circular  valve  19,  engages  with  a  sleeve  21  on  the  piston, 
and  moves  in  a  peculiar  shaped  groove  shown  which  causes  the 
valve  to  partially  rotate  around  the  pin  20,  alternately  opening 
and  closing  the  exhaust  and  admission  ports.  The  valve  has  a 
"bell  topper"  device  which  is  a  cap  to  reduce  air  pressure  on  the 
back  of  the  valve.  The  pin  20'  keeps  the  sleeve  from  revolving 
with  the  piston  so  that  it  merely  reciprocates  with  it.  This 
device  works  with  little  friction  or  jar  as  the  valve  is  nearly  bal- 
anced and  is  only  rotated  around  a  center  and  not  moved  bodily. 
The  air  ports  run  along  the  side  of  cylinder  instead  of  along  the 
top,  and  the  exhaust  is  on  the  top  of  cylinder.  The  section  Fig. 
13  and  illustration  Fig.  14  give  a  good  idea  of  this  drill. 

Mr.  Taylor  Horsfield,  of  Bendigo,  lately  manufactured  for 
Messrs.  C.  R.  McKenzie  and  Company,  Government  Contract- 
ors, of  New  South  Wales,  a  drill  of  this  type  of  exceptionally 
large  proportions,  which  is  to  be  used  in  drilling  holes  of  18  in. 
diameter  in  rock  about  30  ft.  or  40  ft.  under  water.  The  drill, 
which  weighs  one  and  a  quarter  ton,  has  a  cylinder  with  a 
diameter  of  8  in.  with  12-in.  stroke.  This  is  said  to  be  the 
largest  of  its  kind  ever  manufactured.  It  is  made  on  the  same 
pattern  as  Horsfield's  "National"  drills,  which  are  in  common 


22 


ROCK  DRILLS 


FIG.  14.  —  Taylor  Horsfield's  rock  drills. 


STANDARD   PISTON   DRILL 


23 


use  in  mines  throughout  Australia.  The  holes  that  are  to  be 
drilled  by  it  are  in  connection  with  the  erection  of  wharves,  etc. 
The  drilling  rods  weigh  12  cwt. 

The  Holman  Tappet  Drill.  —  The  sectional  illustration  of  this 
drill  in  Fig.  15  clearly  shows  its  construction,  and  the  action 
requires  but  little  explanation.  The  valve  is  of  the  ordinary  D 
type  as  used  in  most  small  steam  engines,  the  tappet  taking  the 


FIG.  15.  —  Holman  tappet  valve  drill. 


place  of  the  valve-spill  or  rod,  and  the  piston  ball  doing  the  work 
of  the  eccentric.  The  working  fluid  passes  alternately  from  each 
end  of  the  valve  into  the  ports,  exhausting  around  the  tappet 
into  the  cylinder  between  the  pistons  and  thence  to  the  atmos- 
phere. The  length  of  stroke  can  be  varied  at  will  by  turning  the 
handle  and  feeding  the  cylinder  towards  the  rock.  The  same 
manufacturers  turn  out  a  tappet  quarry  drill,  which  has  special 


FIG.  16.  —  Climax  tappet  valve  machine. 

advantages  for  deep  boring.  A  large  diameter  is  given  to  the 
front  cylinder  for  lifting  the  bit,  and  by  this  means  holes  are 
commonly  bored  to  a  depth  of  from  30  to  40  ft.  For  working 
tappet  drills  by  steam,  a  blow-through  cock  is  generally  fitted 
to  the  machine  to  get  rid  of  excessive  moisture  in  the  pipe  line. 

Stephens  Climax  Tappet  Valve  Drill.  —  In  this  type  of  drill 
the  tappet  and  valve  are  combined.  Fig.  16  is  one  of  the  later 
types  of  this  drill. 


24  ROCK  DRILLS 

Air  Valve  Drills 

Examples  of  air  valve  machines  include  the  new  Ingersoll 
Eclipse  drills;  the  Rand  Slugger  and  Konomax  drills;  the  Sullivan 
differential  valve  drill;  the  Stephens  Climax  Imperial;  the  Wood, 
McKeeinan,  Little  Hercules,  Hardy,  and  others. 

In  these  machines  the  disadvantages  connected  with  the  use 
of  a  D  slide  valve  are  avoided;  the  valve  being  of  the  "piston" 
or  " spool"  type.  As  in  some  designs  of  the  Slugger,  and  in  the 
Climax  Imperial  the  valve  can  be  adjusted  to  use  air  expansively. 
It  can  also  be  set  to  strike  a  free  blow  by  not  closing  exhaust 
port  until  the  stroke  is  finished.  Such  machines  can  be  made  to 
drill  very  fast  in  certain  rock  when  the  air  does  not  contain  too 
much  moisture. 

Trouble  with  these  types  of  machines  is  liable  to  arise  from 


FIG.  17.  —  Ingersoll  "Eclipse"  drill. 

wear  in  the  cylinder  piston.  When,  despite  the  rings,  leakage 
of  air  develops  from  one  end  of  the  cylinder  to  the  other,  the 
valve  becomes  irregular  in  its  action;  cut-off  is  late,  while  both 
valve  and  piston  " cushion."  The  valve  " nutters"  or  moves  on 
short  stroke  and  the  machine  becomes  inefficient  until  the  cylinder 
is  relined  or  bored  out  to  fit  a  new  piston.  It  is  claimed  for  the 
Slugger  drill  that  owing  to  the  valve  being  moved  by  the  closing 
of  exhaust  ports,  wear  and  leakage  tend  only  to  lengthen  the 
stroke.  In  the  Climax  drill  made  by  Stephens  this  difficulty  is 
met  by  placing  two  circular  conical  leather  valve  seats  in  the 
top  of  the  cylinder  below  the  valve  chest.  These,  though  called 
auxiliary  valves,  do  not  move  at  all  and  might  perhaps  better 
be  called  "rubbing  contacts,"  as  their  use  is  always  to  make  a 
close  rubbing  contact  with  the  piston,  whatever  the  wear,  thus 
preventing  any  leakage  of  air  at  the  wrong  moment  into  their 
ports  to  reverse  the  valve.  Thus  the  valve  motion  is  kept  regu- 


STANDARD  PISTON   DRILL  25 

lar.  This  object  is  satisfactorily  attained  in  practice  by  this 
device.  Wear  on  the  leathers  is  taken  up  by  pressing  them 
down  with  washers  put  in  on  the  top,  face  down,  by  tightening 
the  nuts  on  the  bolts  holding  on  the  valve  chest.  Leakage  past 
the  valve  itself  does  not  render  its  action  irregular. 

Ingersoll  Eclipse  Drill.  —  In  this  drill  the  valve  is  thrown  over 
by  live  air  leaking  past  the  ends,  and  by  means  of  the  recess 
in  the  piston,  the  ends  of  the  valve  are  alternately  opened 
to  exhaust  through  the  space  between  piston  and  cylinder,  and 
through  two  holes,  A  and  B,  Fig.  17,  bored  through  the  cylinder 
walls,  to  the  outside. 

"Little  Hardy"  Rock  Drill  — The  sectional  illustration,  Fig. 
18,  shows  the  general  arrangement  of  the  " Little  Hardy"  drill. 


FIG.  18.  —  Section  of  "Little  Hardy"  rock  drill. 

According  to  the  makers  the  salient  feature  of  the  construction 
is  the  circular  distributing  valve  which  is  thrown  over  by  live 
air,  fed  to  the  end  valve  pistons  by  special  ports  in  constant 
communication  with  the  main  inlet.  There  are  no  tappets, 
guide-bolts,  or  other  mechanical  connections  between  the  valve 
and  the  drill  piston.  Consequently  there  is  nothing  to  lessen 
the  force  of  the  blow  or  to  cause  battering  and  breakage  to  any 
part  of  the  valve  motion. 

The  makers  claim  the  following  advantages  in  this  system: 
"The  valve  is  automatically  locked  in  its  position  by  the  full 
air  pressure  acting  upon  the  whole  surface  of  one  of  the  end 
valve  pistons,  the  opposite  one  being  open  to  complete  exhaust. 
Variable  valve  speed,  due  to  wear  or  fluttering  of  the  valve  in 
other  systems,  is  impossible  in  'Little  Hardy'  drills.  The  valve 
is  unique  in  speed  of  travel,  being  thrown  at  full  pressure." 


26 


ROCK   DRILLS 


STANDARD   PISTON   DRILL 


27 


Taylor  Horsfield's  New  Type  Ingersoll  Drill.  —  This  drill,  Fig. 
19,  is  of  Australian  manufacture,  and  of  the  air-moved  type,  with 
a  valve  motion  similar  to  the  Ingersoll  Eclipse  drill,  only  the 


•e 


valve  is  placed  across  the  cylinder  and  not  longitudinal  with  it. 
The  rotation  device  is  similar  to  that  in  use  on  the  Sullivan  drills. 
Taper  chucks  are  used  exclusively. 

The   Sullivan   Differential    Valve   Rock   Drill.  —  The   especial 
feature  of  the  Sullivan  differential  valve  drill,  Figs.  20  and  21, 


28 


ROCK   DRILLS 


FIG.  21.  —  Sullivan  differential  valve  rock  drill  on  adjustable  tripod. 


STANDARD   PISTON   DRILL  29 

according  to  the  makers,  is  the  spool  pattern  of  the  valve,  Fig.  22, 
with  its  surfaces  so  proportioned  as  to  secure  a  differential  effect 
original  in  this  machine.  Its  action  is  instantaneous,  exact,  and 
uniform;  it  permits  the  length  of  the  stroke  and  the  force  of  the 
blow  to  be  regulated  to  the  best  advantage,  depending  upon  the 
local  conditions.  Thus,  in  starting  a  hole,  or  in  seamy  ground, 
the  drill  may  be  cranked  down  to  give  a  short  stroke  and  a  light 
blow;  while  in  hard,  solid  rock,  the  full  stroke  secures  a  blow  of 
great  strength.  Full  steam  or  air  pressure  on  the  return  stroke, 
or  recover,  causes  proper  mudding  of  the  hole  under  all  circum- 
stances. The  valve  itself  is  simple,  strong,  and  rarely  breaks. 
Its  action  is  not  affected  by  wear  in  other  parts  of  the  drill; 
and  it  works  equally  well  with  steam  or  air. 


FIG.  22.  —  Sullivan  differential  spool  valve. 

The  Rand  "Slugger"  Rock  Drill  — The  "Slugger"  rock  drill 
is  a  machine  designed  especially  for  heavy  work  and  rapid  drilling 
in  mine  and  tunnel  headings.  It  can  be  successfully  operated 
only  with  compressed  air. 

The  " Slugger"  has  an  " air-thrown"  piston  or  spool  valve, 
Fig.  23,  traveling  in  a  reamed  valve  chest  with  a  maximum  move- 
ment of  not  more  than  three-quarters  of  an  inch.  Buffers  at  the 
ends  of  the  valve  chest  receive  the  impact  of  the  valve  at  the 
end  of  its  travel.  The  valve,  being  perfectly  balanced,  is  subject 
to  no  tendency  to  wear  unevenly  and  has  a  free,  easy  movement. 
It  is  of  hardened  steel,  carefully  ground  to  a  working  fit  in  the 
valve  chest  bore. 

The  valve  mechanism  of  the  "Slugger"  is  such  that  it  strikes 


30 


ROCK   DRILLS 


an  uncushioned  blow,  due  to  retarding  the  reversal  of  the  valve 
until  the  blow  is  struck;  the  lower  exhaust  port  is  thus  held  full 
open  during  the  complete  down  stroke.  At  the  same  time  the 
action  of  the  valve  permits  of  the  usual  variation  in  length  of 
stroke  that  is  necessary  in  rock  drills. 

The  "33  type"  is  a  late  model  of  this  machine.  In  this  type, 
the  upper  as  well  as  the  lower  exhaust  port  is  controlled  by  the 
piston  valve  and  the  necessary  cushion  is  afforded  by  live  air 
pressure,  the  exhaust  remaining  full  open  to  the  end  of  the  stroke. 
The  result  is  a  dead,  uncushioned  blow.  A  distinctive  feature 
of  this  type  of  drill  is  the  device  whereby  the  throw  of  the  main 
valve  is  caused  by  the  closing  instead  of  by  the  opening  of  an 
auxiliary  port.  The  result  is  that  the  wear  of  piston,  cylinder, 
etc.,  tends  to  lengthen,  instead  of  shorten,  the  stroke. 


FIG.  23.  —  Rand  "Slugger." 


The  "Slugger"  drill  is  a  rapid  driller  and  a  reliable  machine, 
striking  a  dead,  powerful  blow  while  still  retaining  a  quick  return, 
and  especially  adapted  for  work  in  hard,  solid  rock  where  the 
cushion  effect  on  the  down  stroke  is  not  required  and  where  air 
pressures  are  high. 

Corliss  Valve  Drills 

Torpedo  Drill.  —  The  only  example  of  this  style  of  drill  used 
in  practical  work  that  I  know  of  was  one  designed  by  Mr.  D.  A. 
Foote  of  California.  It  was  named  the  " Torpedo"  drill,  Fig.  24; 
I  believe  it  was  abandoned  owing  to  the  enormous  wear  on  the 
tappets,  connecting  rods,  and  pins.  Remarkable  results  were, 
however,  attained  with  new  drills,  and  for  certain  work  I  believe 
a  drill  of  this  type  with  Corliss  valves  worked  by  air  pressure 
from  auxiliary  valves  might  give  excellent  results. 


STANDARD  PISTON   DRILL  31 

Auxiliary  Valve  Drills 

Two  examples  of  this  type  are  the  Ingersoll-Sergeant  machine, 
which  was  the  pioneer,  and  the  Holman  machine. 

Ingersoll  Sergeant  Drill.  —  "The  auxiliary  valve  is  a  successful 
combination  of  the  independent  air- thrown  valve  of  the  piston  or 
spool  type";  or  in  the  case  of  the  Holman  machine  of  a  D-slide 
valve  having  a  concave  seat  with  piston  ends  and  an  improved 
modification  of  the  tappet  action.  It  retains  certain  advan- 
tages while  avoiding  defects  of  both  valve  movements.  This 
valve  movement  is  one  in  which  the  strains,  shocks,  and  jars  to 
which  the  tappet  is  subjected  are  transferred  from  the  main 
valve  Avith  its  vital  and  delicate  functions  to  small,  light  auxiliary 
valve,  or  valves,  which  "are  designed  to  withstand  this  service 
to  the  best  advantage  and  which  are  cheaply  replaced  when  worn." 


FIG.  24.  —  Foote  torpedo  drill. 


The  movements  of  such  valves  are  quite  free  and  short,  thus 
"the  auxiliary  valve  is  simply  a  trigger  that  releases  the  main 
valve."  These  drills  can  be  run  on  a  very  short  stroke  rendering 
the  starting  of  a  hole  easy,  enabling  the  drill  bit  to  be  driven 
past  heads  and  slips  in  the  rock  which  would  deflect  the  hole 
were  they  attacked  with  long  glancing  blows.  They  are  designed 
to  strike  a  free  uncushioned  blow  on  the  rock,  and  do  so  when 
wear  is  not  excessive,  as  the  exhaust  port  at  the  front  end  is  kept 
open  until  after  the  blow  has  been  struck.  All  makes  of  drill  are 
designed  to  cushion  on  the  return  stroke;  when,  with  any  design 
of  spool  or  piston  valve,  the  piston  begins  to  knock  on  the  back 
stroke,  it  is  a  sign  that  leakage  is  taking  place  between  valve  and 
valve  chest. 

The  auxiliary  valve  drill  has  the  capacity  of  working  with 


32 


ROCK  DRILLS 


very  small  number  of  bits,  which  is  also  advantageous  where 

the  supply  of  drill  bits  is  lim- 
ited and  it  is  hard  to  get  one 
of  just  convenient  length  to 
insert,  or  where  a  bit  so  long 
that  the  machine  must  work 
at  first  on  a  very  short  stroke. 
One  great  advantage  with  this 
machine  lies  in  the  fact  that 
piston  and  cylinder  wear  do 
not  interfere  with  the  valve 
action  owing  to  any  leakage 
between  them.  The  steel  balls 
on  the  Holman  drill  have 
almost  no  wear,  while  wear  on 
the  arc  valve  of  the  Sergeant 
drill  is  compensated  by  renew- 
ing liners,  placed  between  the 
air  chest  and  the  cylinder, 
which  lowers  the  auxiliary 
valve  into  fuller  contact  with 
the  piston. 

The  piston  B  of  the  Ser- 
geant drill,  Fig.  25,  has  in  it  a 
recess  forming  two  shoulders. 
These  engage  the  ends  of  the 
auxiliary  valve  A  and  throw 
it  over  as  one  end  always  pro- 
jects into  the  cylinder.  This 
arc-shaped  valve  has  a  recess 
R  cut  in  it.  In  the  seat  in 
which  the  valve  moves  are 
three  ports;  the  two  end  ones 
P  and  P'  lead  to  the  spaces 
at  the  ends  of  the  main  valve. 
The  other  leads  to  the  exhaust 
port  E.  In  the  figure  the  port 
P'  is  in  communication  with 

the  exhaust.     The  piston  has  just  finished  its  return  stroke  and 
the  main  valve  has  the  port,  leading  to  the  back  of  the  cylinder, 


STANDARD  PISTON   DRILL  33 

open  to  exhaust.  It  will  now  be  thrown  over  admitting  live  air 
to  the  rear  of  the  piston,  and  open  the  exhaust  port  leading  to 
the  front  of  the  piston.  Pressure  to  throw  the  valve  over  is 
gained  by  allowing  live  air  to  leak  past  the  ends  of  the  main 
valve  to  act  on  the  end  surfaces.  It  will  be  seen  that  the  action 
of  the  valve  in  the  Holman  machine  is  practically  the  same. 

This  type  of  valve  has  several  important  advantages  over 
the  other  types  with  the  exception,  perhaps,  of  air-valve  drills 
having  some  compensating  device  for  cylinder  wear.  These, 
theoretically,  having  fewer  wearing  parts  should  work  with  less 
friction  and  be  rapid  drillers.  It  is  wise  in  examining  the  merits 
of  various  valve  devices  always  to  investigate  closely  what  effect 
wear  and  leakage  will  have  upon  them.  It  will  then  be  noticed 
that  many  advantages  claimed  would  not  be  realized  in  practice. 
Where  the  travel  of  the  piston  regulates  the  point  of  cut-off  in 
drills  using  air  expansively,  leakage  between  piston  and  cylinder 
will  generally  make  the  cut-off  later.  Comparing  the  valve 
action  of  the  Holman  with  the  Ingersoll  machine  it  will  be  noted 
that  the  Ingersoll  valve  works  with  less  friction  and  requires  less 
frequent  lubrication,  while  the  Holman  valve,  being  really  a 
Z)-slide  valve  with  cylindrical  seat,  retains  its  seat  and  freedom 
from  leakage  for  a  much  longer  period,  thus  requiring  a  smaller 
sum  spent  for  repairs.  Spool  valves  are  now  fitted  if  required  in 
Holman  machines.  A  spool  valve,  properly  hardened  and  ground 
to  fit,  should,  under  good  conditions,  run  nearly  six  months  before 
requiring  replacement  by  a  larger  size  and  the  chamber  to  be  bored 
out.  With  bad  usage,  in  the  presence  of  grit,  this  may  have  to 
be  attended  to  oftener. 

The  Holman  Auxiliary  Ball-Valve  Drill.  —  The  construction 
of  this  drill  is  shown  in  Fig.  26.  When  the  piston  a  is  at  the  rear 
end  of  the  cylinder,  it  will  have  raised  the  ball  valve  c  and  allowed  d 
to  drop  on  the  valve  seat.  The  result  is,  that  the  air  in  the  end  of 
the  valve  chest  e  has  been  exhausted,  and  passing  through  a  small 
groove  in  the  bottom  of  the  valve  chest  at  the  opposite  end,  it 
forces  the  valve  forward.  This  places  the  fluid  in  communication 
with  the  main  ports.  The  pressure  then  passes  through  the  port 
g  and  drives  the  piston  forward,  whilst  the  previous  admission  at 
the  opposite  end  exhausts  through  h  into  the  exhaust  port  j. 
The  process  is  reversed  for  the  return  stroke.  As  the  piston  moves 
inwards  the  ball  valve  c  drops  on  its  seat,  and  the  air  passes 


STANDARD   PISTON   DRILL  35 

through  the  groove  filling  the  space  at  e;  as  the  valve  chest 
at  /  has  been  exhausted,  the  valve  moves  in  the  opposite 
direction. 

The  ball  valve  and  buffer  valve  require  no  adjustment  and 
resist  wearing.  The  main  valve  is  of  the  ordinary  D  type,  and 
consequently  the  live  fluid  cannot  pass  over  into  the  exhaust. 
In  order  to  eliminate  the  friction  and  maintain  the  speed  neces- 
sary, the  valve  chest  is  a  steel  casting  hardened  and  ground;  the 
valve  is  also  hardened.  No  adjustment  of  the  air-locking  device 
is  required,  consequently  the  drill  will  work  with  slacker  piston 
than  is  possible  with  most  drills.  The  balls  controlling  the  valve 
exhaust  are  made  of  the  hardest  crucible  steel.  The  movement 
of  the  piston  in  its  backward  and  forward  stroke,  and  the  twist 
motion,  tend  to  keep  the  ball  revolving,  thus  presenting  a  large 
wearing  surface.  These  balls  are  practically  indestructible. 

ROTATION  SYSTEMS  ON  PISTON  ROCK  DRILLS 

Slip  Rotation.  —  Many  makers  have  copied  the  Sergeant  sys- 
tem of  slip  rotation,  Fig.  27,  which  is  described  by  the  makers 
as  follows: 

"The  Sergeant  slip  rotation  is  one  of  the  most  valuable  fea- 
tures of  these  drills,  permitting 
the  machine  to  free  itself  in  a 
binding,  caving  material  without 
injury  to  steels  or  piston.  It  is 
applied  on  all  but  the  'Eclipse' 
type  of  drill.  The  ratchet  is  held 
by  friction  between  the  washer 

and  the  back  head,   under  pres-      fta.  27.  —  Sergeant  slip  rotation, 
sure  of    the   cushion   spring.     It 

is  thus  free  to  slip  when  the  steel  l  glances '  or  twists  backward, 
freeing  the  bar  from  twisting  strains;  and  by  changing  the 
spring  tension,  the  friction  effect  may  be  varied  to  meet  dif- 
ferent service  requirements.  The  ratchet  and  pawls  are  case- 
hardened,  and  the  device  is  one  of  great  durability  and 
strength."  In  this  type  the  pawls  are  pressed  out  by  cylin- 
drical coil  springs. 

In  the  Stephens  drills  the  slip  rotation  is  employed;  in  this  as 
well  as  in  the  Little  Hardy  drills,  springs  can  be  replaced  through 
stud  holes.  Generally  speaking,  in  all  standard  types  of  drills, 


36 


ROCK   DRILLS 


rotation  gives  little  trouble  except  that  occasionally  a  badly  tem- 
pered lot  of  springs  may  be  met  with. 

Modified  Slip  Rotation.  —  In  the  Sullivan  drills  the  rotation 


FIG.  28.  —  Sullivan  rotating  device. 

device  is  modified,  and  is  described  by  the  makers  as  follows: 
"The  drill  steel  is  given  the  necessary  rotation,  to  preserve  the 
cylindrical  shape  of  the  hole,  by  a  rifle  bar,  extending  into  the 
top  of  the  piston,  Fig.  28,  and  terminating  at  its  upper  extremity 


FIG.  29.  —  Holman  ratchet  and  pawls 

in  a  ratchet  head.  Rotation  occurs  on  the  up  stroke.  The  fric- 
tion between  the  top  head  and  the  ratchet  ring  and  collar  is 
such  as  to  permit  the  ring  to  slip  in  case  the  drill  steel  becomes 
wedged  in  the  hole,  thus  precluding  damage  to  the  mechanism. 


STANDARD   PISTON   DRILL 


37 


The  whole   device  is  unusually  effective  and  durable,  and  will 

outwear  four  of  any  other  pattern.     The  ratchet  head  and  rifle 

bar  are  milled  out   of  a  solid 

piece  of  tool  steel  and  hardened 

in  oil.      Rounded  surfaces  and 

hardened  steel  pins   or   rollers 

provide  the  ratchet  movement, 

instead  of  the  thin  teeth   and 

pawls  sometimes  employed." 

Pawl-and-Ratchet     Rotation. 

-  The  makers  of  the  Holman 

drills  employ  the  non-slipping 


FIG.  30.  —  Rand  rotation,  showing 
upper  head  removed,  rotative  bar 
and  pawls  in  place. 


type  as  shown  in  Fig.  29. 

The  Rand  "  Little  Giant" 
has  a  similar  system,  Fig.  30,  and  the  makers  describe  it  as  follows  : 
"Two  pawls,  Fig.  31,  engage  at  once,  thus  distributing  the  strain 


2637 


FIG.  31.  —  Pawls. 


between  two  pawls  and  two  ratchet  teeth.  The  inserted  pawl 
requires  no  studs,  but  fits  in  a  bored  recess  in  the  ratchet  box 

with  a  very  large  bearing  sur- 
face.    Wear  is  thus  reduced 
and  a  long  life  assured.   There 
is  no  pin  to  break  or  wear. 
The  pawl  is  a  solid  drop  forg- 
FIG.  32.  — Rotating  bar,  "Little  Giant"     ing  of  selected  steel,  properly 
drill.  hardened.     The  bearing  por- 

tion is  of  large  diameter.  A  flat  spring  holds  the  pawls  to  their 
seat.  The  rotating  bar,  Fig.  32,  is  of  high-carbon  steel  and  works 
in  a  bronze  rotating  nut.  It  is  carried  through  the  ratchet,  giving  a 


38 


ROCK   DRILLS 


back  bearing  of  large  diameter  in  the  ratchet  box.  The  ratchet 
is  of  hardened  steel,  pressed  and  keyed  on  the  rotating  bar.  The 
upper  head  and  ratchet  box  cover  the  entire  rotation,  excluding 
dust  and  dirt." 

DESIGN  OF  FRONT  OR  LOWER  HEADS 

For  use  with  air,  nearly  all  machines  use  the  type  of  head,  first 

introduced  by  the  Rand  Drill 
Company.  "  In  this  style  the 
split  malleable  head,  Fig.  33, 
is  bored  to  receive  a  split  bush- 
ing of  cast  iron,  accurately  fit- 
ting the  chuck  rod.  A  cup 
leather  held  in  the  rear  be- 
tween bushing  and  head  fur- 
nishes the  packing  necessary. 
All  strain  on  the  head  proper 
is  taken  up  by  the  taper  fit  of 
the  steel  ring  over  the  head 

FIG.    3.-C&H  ring  lower  head-parts   under  the  tension  of  the  side 
assembled  and  separate. 

rods  and  buffer.   The  bushings 

may  be  renewed  and  replaced  when  worn. 
Some  machines,  and  especially  those 
in  which  steam  is  used  still,  employ  front 
heads  similar  to  those  shown  in  Type 
"15,"  Fig.  34,  of  the  Rand  Drill  Com- 
pany, which  is  described  as  follows:  "A 
selected  metal  is  used  for  the  front  and 
lower  heads.  The  joints  between  head 
and  cylinder  are  ground  —  no  gasket  or 
packing  is  used.  This  front  head  is  made 
in  two  types:  one,  for  steam,  has  a  gland 
and  proper  stuffing-box;  the  other,  for 
air,  has  a  cup  leather.  The  steam  head 
may  be  used  for  air,  but  steam  must 
never  be  used  with  the  air  head.  Both 
patterns  are  long  and  reamed  to  perfect 
trueness,  giving  an  ample  piston  guide. 
Powerful  through-bolts  hold  them  in  place 
and  transfer  all  stresses  directly  to  the  cushion  springs  in  the  rear.' 


FIG.  34. —  The"  15 "type 
front  head,  steam  and  air 
patterns. 


STANDARD   PISTON   DRILL 


39 


DRILL  MOUNTINGS  AND  FITTINGS 

The  following  views  of  arms,  bars,  and  saddles  or  clamps  as 
made  by  two  leading  makers  show  the  construction  of  three 
parts  clearly.  The  following  description  is  taken  from  a  paper 
by  Arthur  H.  Smith,  " Machine  Drills  for  Hard  Rock."  It  con- 
cisely describes  the  various  mountings  used  in  mines. 

"Drill  Clamp.  —  The  cylinder  of  a  rock  drill  slides  in  a  guide 
or  cradle,  Fig.  35,  which  in  turn  is  mounted  on  a  stretcher  bar, 
tunnel  column  or  tripod,  etc.,  according  to  the  work  to  be  done. 
The  actual  attachment  consists 
of  a  powerful  jaw  chuck  or  cone 
clamp  which  holds  the  bottom  of 
the  cradle  and  is  in  turn  saddled 
round  the   bar   or   column   and 
secured  to  it  by  a  cap  and  bolts. 
The  adjustments  of  the  drill  and 
saddle  are  independent  of   each 
other,  and  the  drill  can  revolve 
on  its  seating  for  setting  in  any 
direction. 

"This  fact  is  taken  advan- 
tage of  in  coal  mines  and  dimen- 
sion stone  quarries,  where  a  lever 
handle  is  sometimes  attached  to 
the  machine  for  conveniently  im- 
parting a  swinging  action  to  it,  the  clamp  nut  of  the  mounting 
being  given  just  sufficient  tension  to  hold  the'  machine  firmly 
without  impeding  the  lateral  movement.  Thus,  by  gradually 
swinging  the  machine  across  the  face  during  work,  the  cutting 
bit  strikes  each  blow  in  close  proximity  to  the  previous  one,  the 
outcome  being  a  straight  cut  or  nick  right  across  the  face. 
Generally  each  cut  from  one  fixing  is  from  10  to  12  ft.  in  length 
by  from  4  to  6  ft.  deep  and  from  2|  in.  to  3  in.  across  according 
to  the  size  of  the  cutting  bits  employed.  Some  makers  employ 
a  worm  gearing  operated  by  handle  to  produce  this  swinging 
movement.  The  cutting  bits  used  in  connection  with  these 
machines  in  coal  measures  are  usually  provided  with  several 
radially  disposed  teeth,  an  odd  number  being  employed  to 
prevent  sticking. 


FIG.  35.  —  Sullivan  guide  or  cradle. 


40  ROCK  DRILLS 

"  Stretcher  Bar.  —  For  drifts  of  small  dimensions,  for  winze 
work  and  for  sloping,  the  rock  drill  is  generally  clamped  to  a 
single  screw  column,  Figs.  36  and  38,  or  stretcher  bar.  The 
usual  length  is  6  ft.  with  jack  screw  in,  the  latter  increasing  the 


Single  jack  bar.  Double  jack  bar. 

FIG.  36.  —  Ingersoll-Sergeant  rock  drill  column. 

length  about  10  in.     The  diameter  of  the  bar  is  from  3  to  5  in. 
according  to  the  machine  employed. 

"Double  Screw  Tunnel  Column.  —  For  larger  drifts  and  tun- 
nels double  jack  screw  columns,  Figs.  36  and  37,  are  employed, 
these  being  of  sufficient  strength  to  support  two  machines.  The 
drill  is  saddled  on  a  steel  cross  arm,  which  in  turn  is  clamped  to 
the  column.  By  means  of  a  safety  clamp,  or  collar,  which  is 
placed  immediately  below  the  arm  clamp,  the  arm  may  be  loosened 


STANDARD   PISTON   DRILL 


41 


FIG.  37.  —  Sullivan  drill  on  double  screw,  a  jack,  mining  column. 


FIG.  38.  —  Sullivan  drill  on  single-screw  mining  column,  or  shaft  on 
stopping  bar. 


42 


ROCK   DRILLS 


and  the  drill  swung  out  of  the  way,  and  swung  back  without  losing 
alignment  when  drilling  is  to  be  resumed.  For  holes  on  a  lower 
level,  the  safety  clamp  is  first  lowered  to  the  desired  point,  after 
which  the  arm  is  loosened,  and  the  arm  with  the  machine  attached 
is  slid  to  the  place  without  unnecessary  labor.  The  double 
screw  column  is  usually  4J  in.  diameter  by  7  ft.  long,  with  10-in. 


FIG.  39.  —  Tripod  for  mounting  drills  in  open  air  or  large  stopes. 

jack  screws  drawn  in.     Wood  blocking  is  used  above  and  below 
the  columns  to  secure  a  firm  hold. 

"  Tripod.  —  For  general  outdoor  work  and  for  operations  in 
mines  where  drifting  columns  have  no  application,  the  rock  drill 
is  clamped  to  a  tripod  stand,  Fig.  39.  A  universal  joint  permits 
the  legs  of  the  stand  to  be  adjusted  to  any  desired  angle  or  posi- 
tion. Moreover,  the  legs  are  telescopic  and  may  be  lengthened 
or  shortened  at  will.  The  machine  can  thus  be  quickly  set  up 
no  matter  how  irregular  the  ground,  or  how  awkwardly  situated 
the  surface  to  be  drilled.  Detachable  weights  are  hung  to  the 


STANDARD  PISTON   DRILL  43 

legs  to  steady  the  machine  during  operation,  these  weights  vary- 
ing from  150  Ib.  to  400  Ib.  per  set  of  three,  according  to  the  size 
of  the  machine. 

"A  variation  of  the  standard  tripod  is  found  in  the  Lewis 
type,  which  is  employed  where  three  or  four  holes  are  required 
to  be  put  down  close  together  and  parallel  to  each  other.  The 
general  arrangement  of  this  stand  only  differs  from  that  of  the 
last  described  by  the  addition  of  a  planed  and  slotted  front  bar 
which  gives  the  drill  a  lateral  movement  of  from  6  to  9  inches. 
Several  holes  can  thus  be  bored  parallel,  and  the  standing  rock 
between  the  holes  can  be  cut  out  by  a  special  flat  broaching  bit 
without  change  of  position. 

"Rock  Drill  Carriages.  —  Various  forms  of  drill  carriages  to 
mount  either  two  or  four  machines  have  been  used  for  tunneling. 
One  type  consists  of  a  vertical  externally  screwed  column  carried 
on  a  small  trolley.  Two  horizontal  arms  are  mounted  on  the 
column,  and  upon  these  arms  are  saddled  the  drills.  The  trolley 
is  run  up  to  the  face,  the  column  jacked  tight  against  the  roof, 
the  arms  set  to  the  required  positions  and  jacked  to  the  walls. 
The  raising  and  lowering  of  the  arms  on  the  secured  column  is 
effected  by  means  of  worm  gear  and  handle.  Another  type  of 
carriage  is  a  steel  girder  framework  mounted  on  wheels  and  carry- 
ing two  vertical  stretcher  bars,  each  supporting  one  or  two  drills. 
The  frame  and  stretcher  bars  are  so  disposed  that  a  truck  can 
be  run  through  and  up  to  the  face  to  facilitate  the  removal  of 
debris. 

"Rock  drill  carriages  have,  however,  been  almost  entirely 
superseded  by  tunnel  columns,  as  in  the  case  of  the  former  either 
the  whole,  or  a  considerable  part,  of  the  debris  from  the  previous 
blast  must  of  necessity  be  removed  to  clear  the  track,  and  to 
enable  the  laying  of  fresh  lengths  of  rail  before  the  carriage  can 
again  run  up  to  the  face,  whilst  with  the  latter  only  the  small 
space  necessary  to  set  up  the  column  need  be  cleared  and  boring 
recommenced  almost  simultaneously  with  the  removal  of  debris. 

"Shaft  Sinking  Frame.  —  Heavy  expenditure  must  always 
accompany  the  sinking  of  main  shafts,  the  diameter  of  which  the 
present  tendency  is  to  increase,  and  it  follows  that  those  in  charge 
of  the  work  are  anxious  to  increase  the  speed  of  boring  as  much 
as  is  mechanically  possible.  In  large  main  shafts  stretcher  bars 
cannot  be  employed  for  mounting  the  machine  drills,  and  under 


44 


ROCK   DRILLS 


certain  conditions  tripods  are  somewhat  impracticable  owing  to 
the  time  lost  in  lowering  and  adjusting  plant,  and  raising  it  to 


FIG.  40.  —  Shaft-sinking  frames. 

surface  preparatory  to  blasting  operations.  Shaft-sinking  frames, 
Fig.  40,  have,  under  these  conditions,  been  found  of  considerable 
service.  A  useful  type  of  shaft  frame  by  Howarth  and  Larmuth 
may  be  described  as  a  steel  wheel-shaped  center  piece  with  flanged 


STANDARD  PISTON   DRILL  45 

rim,  on  which  a  ring  made  in  halves  is  bolted  and  can  revolve, 
being  supported  between  the  rim  flanges.  In  the  center  piece 
are  three  bosses  through  which  adjustable  legs  are  passed  to 
support  the  frame  on  the  shaft  floor.  Three  or  more  stretcher  bars 
are  hinged  to  the  ring,  provision  being  made  to  fasten  these  bars 
securely  to  it.  The  rock  drills  are  clamped  to  the  stretcher 
bars,  which  are  provided  with  screws  for  jacking  to  the  walls. 
On  the  center  piece,  where  eye  bolts  are  arranged  for  hoisting 
and  dropping  the  frame,  is  a  manifold  tail  for  an  air  pipe,  with 
as  many  branches,  cocks,  and  unions  as  there  are  drills  employed. 
The  plant  is  put  together  at  surface,  lowered  into  position  by 
means  of  a  winch,  and  raised  again  after  completion  of  boring 
the  floor,  thus  abolishing  the  slower  methods  of  clearing  gear  from 
the  shaft  bottom." 

DRILL  CHUCKS 

In  the  chapter  on  repair  and  maintenance  of  drills  the  impor- 
tant part  played  by  the  chuck  in  drilling  economy  has  been 
pointed  out.  The  ordinary  chuck  with  its  cylindrical  liners, 
U-bolt,  nuts  and  pad  or  key  is  illustrated  in  several  drills.  Its 
disadvantages  are:  that  it  takes  some  time  to  insert  and  take 
out  drill  bits;  that  the  removal  of  the  chuck  bushing  when  worn 
is  troublesome.  The  earlier  forms  of  chuck  were  the  one-bolt 
chuck,  which  broke  too  readily  in  large  drills,  and  the  taper  chuck. 
This  chuck  is  still  used  entirely  in  drills  of  Australian  manufac- 
ture. The  chuck  is  bored  out  with  a  taper  recess,  having  a  slot 
cut  through  the  body  of  chuck  for  the  insertion  of  a  wedge  to  be 
hammered  to  loosen  the  drill  when  finished.  The  shank  end  of 
drill  bit  is  made  with  a  corresponding  taper.  This  type  of  chuck 
has  some  important  advantages.  It  always  keeps  the  drill  bit 
centered  true  despite  wear,  and  is  simple.  A  machine  fitted  with 
this  chuck  will  always  out  drill  one  fitted  with  U-bolt  chuck. 
Its  disadvantages  are  that  the  drill  sticks  sometimes,  causing 
vexatious  delays.,  It  is  also  difficult  to  harden  the  taper  end 
of  the  shank  sufficiently  without  making  it  too%  brittle.  The 
Ingersoll-Sergeant  Company  introduced  a  taper  chuck  with  an 
arrangement  of  liners;  but  afterwards  withdrew  it  though  it 
gave  satisfaction  to  users.  Most  manufacturers  are  now  supply- 
ing a  half-bush  chuck,  a  chuck  in  which  half  the  bushing  opposite 
the  pad  or  key  is  removable  by  hand  and  reversible. 


46 


ROCK  DRILLS 


FIG.  41.  —  Maynard  chuck. 


The  Maynard  chuck,  Fig.  41,  illustrates  one  device  of  this 
type;  the  liner  is  not,  however,  reversible,  and  wear  between  the 
wedge  17  and  13  can  only  be  taken  up  by  placing  liners  under  14. 
It  is  described  as  follows: 

"The  chuck  has  two  jaws,  7,  22,  with  rounded  projections  at 

their  front  ends  to  facilitate  in- 

QlUjf^^  sertion  of  the  drill.     The  jaws 
17    \    \  o/  f7  are  mounted  in  the  head  1  and 
— "-  r-^mnl'6   -  are  prevented  from   falling  out 

of,  or  too  far  into,  the  chuck, 
the  jaw,  22,  by  means  of  a  pin- 
held  projection,  23,  passing 
through  a  hole  in  the  head,  and 
the  jaw,  7,  having  longitudinal 
lugs  8  adapted  to  engage  the  edges  of  the  slot,  6,  through  which 
the  jaw  slides.  The  provision  of  a  forward  end,  10,  of  the  jaw,  7, 
prevents  tilting,  and  the  rear  end,  11,  is  beveled  to  facilitate  in- 
sertion. The  jaws  are  closed  by  a  wedge,  17,  with  a  hole,  19,  and 
split-pin  to  prevent  displacement;  the  wedge  engages  a  U-piece, 
13,  passing  through  slots,  12,  in  the  head  and  formed  with  a  wider 
base,  14.  A  cylindrical  recess  may  be  formed  in  the  bottom  of  the 
axial  hole  to  receive  the  end  of  the  drill." 

The  Warren-Tregoning  chuck,  Fig.  42,  appears  to  have  fea- 
tures of  great  merit,  but  has  not  been  largely 
used.     The  end  of  the  piston-rod,  A,  of  the 
drilling  machine  is  enlarged  and  a  dovetail 
hole  made  in  it.     Two  keys,  B,  #,  with  taper 
corresponding  to  that  of  the  dovetail,   will 
just  slip  into  the  hole;  but  when  the  drill  is 
inserted  between  them,  they  are  prevented 
from  falling  out.     When  the  drill  is  put  in 
place,  the  keys,  B,  B,  are  drawn  out  by  a 
pinch-bar,  or  any  other  convenient  tool,  work- 
ing against  their  heads.     Then,  as  soon  as  the 
machine  is  started,  the  shock  of  the  drill  on 
the  rock  tends  to  force  the  keys  outwards,  and 
they  thus  grip  very  firmly.     To  release  the  drill,  it  is  only  neces- 
sary to  strike  one  of  the  keys  sharply  on  the  head  with  a  hammer. 
It  will  be  noticed  that  the  chuck  can  easily  be  adapted  to  different 
sections  of  drill  shank  by  means  of  separate  sets  of  keys. 


FIG.  42.  —  Warren- 
Tregoning  rock  drill 
chuck. 


STANDARD   PISTON   DRILL 


47 


The  chuck  just  used  on  the  Chersen  light  stoping  drill  is 
shown  in  Fig.  43.  Wear  between  wedge  pad  and  ring  must  also 
be  taken  up  by  inserting  liners  on  the  opposite  side  of  ring. 


FIG.  43.  —  Chersen  2|-inch  diameter,  6-inch  strike 
ball  valve  drill,  weight  113  pounds.  Shows 
chuck  which  is  self-tightening. 

Holman  Chuck.  —  The  Holman  chuck  is  shown  in  Fig.  44, 
and  described  as  follows:  It  comprises  a  slotted  piston-rod  end, 
a,  holding  a  half-round  bushing,  c,  between  which  and  a  pad,  d, 


FIG.  44.  —  J.  H.  Holman  chuck. 

the  drill  is  clamped.  The  pad  has  lateral  lugs,  e,  provided  with 
holes,  /,  through  which  passes  a  U-bolt,  h,  holding  nuts,  i,  and 
fixed  by  a  wedge,  j.  The  slot  for  the  pad  and  also  the  pad  and 
separate  half-bushing  extend  to  the  end  of  the  shank. 


48  ROCK  DRILLS 

The  Ingersoll-Rand  Company  has  introduced  a  somewhat 
similar  chuck.  The  Stephens  Chuck  is  one  of  the  simplest  and 
is  also  shown  in  Fig.  147. 

These  chucks  are  a  distinct  advance  on  the  old  style.  They 
allow  a  more  rapid  changing  of  drills;  can  be  renewed  more  easily, 
and  looked  after  better;  hence,  there  is  not  the  excuse  for  trying 
to  bore  holes  with  the  end  of  drill  bits  showing  an  eccentric  move- 
ment of  a  quarter  of  an  inch  in  every  direction.  These  half 
bushings  wear  irregularly  and  should  be  turned  end  for  end  every 
week.  In  some  designs,  liners  may  be  inserted  behind  them  to 
make  up  for  wear. 

The  ordinary  U-bolt  chuck  can  be  modified  by  inserting  a 
wedge  between  the  back  of  the  pad  and  the  U-bolt,  which,  in 
some  cases,  makes  manipulation  quicker.  All  makers  supply  flat- 
backed  pads  for  this  purpose  if  required. 

MATERIALS  USED  IN  PISTON  ROCK  DRILLS 

The  cylinder  shell  and  valve  chest  are  usually  made  of  a 
special  mixture  of  cast  iron.  The  cradle  is  cast  steel.  The 
ratchet  box  and  cover  are  special  rough  steel.  The  piston-rod 
is  solid  open-hearth  steel.  The  valve  is  case-hardened  iron  or 
cast  steel.  The  tappet,  ratchet,  pawl,  and  twist  bar  are  tool 
steel.  The  rotation  nut  is  bronze.  All  bolts,  studs,  feed-screw, 
handle,  nut  and  tool-holder  are  made  of  best  mild  steel.  Some- 
times malleable  cast  iron  is  employed  in  certain  parts.  Pistons 
and  other  parts  are  oil-hardened,  and  some  manufacturers,  espe- 
cially in  the  case  of  hammer  drills,  use  special  alloys,  such  as  of 
nickel-  or  vanadium-steel  for  parts  subject  to  great  vibration. 


Ill 

HAMMER  DRILLS 

THE  use  of  hammer  drills  in  mining  is  quite  a  recent  develop- 
ment, though  the  idea  is  an  old  one.  Instead  of  striking  the 
drill  with  a  hammer  swung  by  hand  the  drill  is  struck  by  a 
piston-hammer  reciprocating  in  a  cylinder.  Such  tDols  were 
first  designed  by  the  mechanical  engineer  to  help  him  in  his 
work  in  calking,  chipping,  and  riveting;  for  this  work  they 
proved  a  great  success.  The  Franke  drill  was,  I  believe,  the  first 
attempt  to  employ  this  method  underground.  It  was  intro- 
duced into  the  Mansfield  copper  mines,  Germany.  That  it  did 
not  prove  a  success  is  readily  understood  when  its  complicated 
mechanism,  is  seen.1  It  had  a  bewildering  number  of  working 
parts  and  was  designed  to  strike  8000  blows  per  minute.  It 
weighs  16  Ib. 

The  development  of  the  hammer  drill  is  closely  associated 
with  the  name  of  George  Leyner,  though  the  chief  development 
has  not  taken  place  quite  along  the  lines  he  started.  His  first 
drill  was  put  on  the  market  1898. 

CLASSIFICATION  OF  HAMMER  DRILLS 

Hammer  drills  may  be  classed  under  several  heads,  as  fol- 
lows: (1)  Those  mounted  on  a  cradle  like  a  piston  drill  and 
fed  forward  by  a  screw;  (2)  those  used  and  held  in  the  hand; 
and  (3)  those  used  and  mounted  on  an  air-fed  arrangement. 
The  last  two  classes  are  often  interchangeable. 

Mr.  Leyner,  though  now  making  drills  of  the  latter  classes, 
was  the  pioneer  of  the  large  3-inch  diameter  piston  machine  to 
be  worked  in  competition  with  large  piston  drills.  The  smaller 
Leyner  Rock  Terrier  drill  was  brought  out  for  stoping  and  driving; 
it  could  not,  apparently,  compete  with  machines  of  other  classes. 

Divided  thus  we  have : 

1.  Cradle  drills  —  Leyner,  Leyner  Rock  Terrier,  Stephens 
Imperial  hammer  drills  and  the  Kimber. 

1 C.  Le  Neve  Forster's  Text  Book  of  Ore  and  Stone  Mining,  p.  192. 

49 


50  ROCK  DRILLS 

2.  Drills  used  only  with  air  feed  —  Gordon  drill   and  the 
large  sizes  of  the  Murphy,  Little  Wonder,  and  others. 

3.  Drills    used   held   in   hand   or   with    air  feed  —  Murphy, 
Flottman,    Cleveland,    Little    Wonder,    Shaw,    Hardy   Nipper, 
Sinclair,   Sullivan,  Little  Jap,   Little  Imp,  Traylor,  and  others. 
Again,  they  may  be  divided  into  those  that  are  valveless,  with  the 
differential  piston  or  hammer  itself  acting  as  a  valve.   The  Murphy, 
Sinclair,  Little  Wonder,  Shaw,  Little  Imp,  Leyner  Rock  Terrier, 
and  Kimber  drills  belong  to  this  class.     The  large  Leyner  drill 
is  worked  by  a  spool  valve  resembling  that  of  the  Slugger  drill, 
Fig.  22;  the  Flottman  by  a  ball  valve;  the  Little  Jap,  by  an  axial 
valve;  the  Gordon  drill,  by  a  spool  valve  set  at  one  end  of  cylin- 
der at  right  angles  to  it;  the  Waugh  and  Sullivan  drills,  by  spool 
valves  set  in  the  same  axial  line  as  cylinder;   the  Hardy  Nipper, 
and  the  Stephens  Imperial  hammer  drills  by  an  air-moved  slide- 
valve  set  midway  on  the  side  of  cylinder;  the  Cleveland  by  a 
spool  valve  set  towards  rear  of  cylinder. 

They  may  again  be  divided  into  those  drills  in  which  the  piston 
hammer  delivers  its  blow  on  the  end  of  the  steel  itself.  A  collar 
is  placed  on  the  drill  to  prevent  it  entering  the  cylinder.  The 
other  class  has  an  anvil  block  or  striking  pin.  This  anvil  block 
fits  into  the  end  of  cylinder  between  piston  and  steel.  It  receives 
and  transmits  the  blow,  also  prevents  the  drill  end  entering 
cylinder. 

Rotation.  —  Different  systems  are  also  employed  to  produce 
rotation  of  drill  steel.  In  the  large  Leyner  machine,  Model  VI, 
this  is  done  automatically  by  a  simple  arrangement  of  expanding 
ring  and  rifle  bar.  In  the  Flottman,  Hardy  "  Nipper,"  and 
Kimber,  it  is  automatic  by  various  devices.  In  the  Leyner  Rock 
Terrier  it  is  positive  and  geared  to  a  feed  screw.  In  the  Gordon 
and  Climax  Imperial  drill  it  is  by  hand,  by  means  of  a  spindle 
provided  with  a  ratchet  or  handle  at  the  rear  of  the  machine. 
In  almost  all  the  other  types  it  is  either  oscillatory,  the  machine 
being  pivoted  on  a  central  spindle,  or,  as  in  the  Hardscogg 
Wonder,  the  whole  cylinder  is  completely  rotated. 

ADVANTAGES  AND  DISADVANTAGES  OF  DIFFERENT  TYPES 

I  give  drawings  and  descriptions  or  illustrations  of  most 
of  these  machines  to  compare  the  advantages  and  disadvantages 
of  the  various  types  for  various  branches  of  mining  work. 


HAMMER  DRILLS  51 

Water  Leyner  Hammer  Drill.  —  A  sectional  drawing  of  Model 
No.  VI,  the  latest  design,  is  shown  in  Figs.  45  and  46. 

The  general  design  is  clear  from  the  cross-section  shown.     It 
will  be  seen  that  an  arrangement  of  buffers  is  provided  to  take 
up  the  energy  of  the  blow  struck 
by  hammer  should  the  head  of 
the  drill  not  be  in  position. 

Rotation  is  effected  by  means 
of  three  strong,  simple  parts  — 
a  rifle  bar,  18;  a  rotating  brake, 
47;  and  a  rotating  ring,  48.  It 
is  entirely  unlike  any  other 
method  and  entirely  eliminates 
all  small,  frail,  complicated  parts, 
such  as  pawls,  pawl  springs, 
plungers,  rollers,  etc.  There  is 
no  toothed  ratchet,  in  the 
machine.  Some  of  the  principal 
parts  are  shown  in  Fig  47. 

The  rotating  brake  fits  over 
the  head  of  the  rifle  bar  inside 
of  the  rotating  ring,  the  rotating 
ring  being  held  firmly  by  ten- 
sion against  the  back  head. 
Turning  the  rifle  bar  to  the  left 
contracts  the  brake  and  allows 
both  brake  and  rifle  bar  to  slip 
freely.  Turning  to  the  right 
expands  the  brake  against  the 
rotating  ring  and  holds  both 
brake  and  rifle  bar  firm. 

The  rifle  bar  fits  into  the 
hammer,  13,  and  the  hammer  into 

the  chuck,  7,  which  in  turn  loosely  accommodates  the  lugs  of 
the  shank  of  the  drill  steel.  The  Leyner  release  rotation  prevents 
accidents  to  the  machine  in  case,  for  any  reason,  rotation  in  the 
proper  direction  is  impeded.  As  explained  above,  the  rotating 
ring,  48,  is  held  against  the  back  head,  28,  by  tension,  which 
is  so  adjusted  that  the  entire  rotating  mechanism  —  rifle  bar, 
rotating  brake,  and  rotating  ring  (and,  necessarily,  hammer, 


52 


ROCK  DRILLS 


HAMMER   DRILLS 


53 


Rotating  plate. 


Back  head.  Back  cindering. 


Rifle  bar,  it  rotates  hammer. 


Pawl  spring. 


Pawl  spring  plunger. 


Shanks  on  drill  steel. 


One  of  four  oblong 
pawls. 


Hammer. 


Chuck  rotated  by  hammers. 
FIG.  47. 


54  ROCK  DRILLS 

chuck,  and  drill  steel),  will  turn  in  the  wrong  direction  in  case 
of  some  excessive  strain  and  before  anything  breaks  or  the  drill 
stops  running. 

The  steels  employed  are  steel  tubes  welded  to  a  specially  hard 
head  having  two  lugs  on  the  shank,  with  a  hollow  high-grade 
steel-cutting  portion  welded  on  the  other  end.  The  two  lugs 
engage  with  the  chuck  and  cause  the  drill  to  rotate  with  it  and 
the  piston.  The  arrangement  enabling  a  spray  of  air  and  water  to 
be  passed  down  the  hollow  steel  to  the  cutting  edge  is  a  vital  one, 
and  is  the  main  cause,  I  believe,  in  the  efficiency  of  the  machine. 
No  dust  is  formed  which  will  affect  the  health  of  the  miners. 
For  a  discussion  regarding  the  merits  and  defects  of  this  type 
of  drill  see  Chapter  VII  on  the  "  Philosophy  of  the  Process  of 
Drilling  Rock."  The  makers  claim  that  it  will  drill  faster  than 
any  piston  drill  of  equal  cylinder  diameter  and  use  20  per  cent, 
less  air.  It  requires  80  to  100  cu.  ft.  of  air  per  minute  at  100  Ib. 
pressure.  It  needs  high  pressures  to  operate  to  advantage.  It 
is  working  in  numerous  mining  fields  in  America;  but  owing  to 
various  causes,  some  of  which  have  little  to  do  with  the  drill  itself, 
it  has  not  so  far  proved  successful  in  hard  rock  like  the  Rand, 
Rhodesia  and  Kalgoorlie.  The  claim  that  drills  can  be  changed 
in  a  very  much  shorter  time  than  those  employed  with  piston 
drills  does  not  hold  to  any  great  extent  against  the  latest  styles 
of  chucks  now  used  in  piston  drills.  An  automatic  lubricator 
is  now  provided  for  use  with  this  machine. 

There  can  be  no  doubt  that  the  Leyner  drill  (particularly  in 
the  last  model  "No.  9  heavy,"  having  side  rods  and  spring  buffers 
to  take  up  blows  of  hammer)  has  established  its  position  as  a 
formidable  competitor  to  the  piston  drill  in  tunnel  driving.  It 
now  holds  the  records  in  the  Elizabeth  Lake  and  Roosevelt  tun- 
nels. 

The  conditions  under  which  it  does  its  best  work  are  those 
evidently  in  which  speed  is  of  far  greater  importance  than  main- 
tenance cost,  and  where  pure  water  is  available  for  use  in  the 
drill. 

Leyner  Rock  Terrier.  —  The  smaller  drill  shown  in  section, 
Fig.  48,  was  recently  introduced  on  the  Rand  as  a  stoping  drill 
for  small  stopes.  It  is  no  more  powerful  than  the  air-feed  types 
of  drill;  is  not  nearly  so  easily  handled  and  so  cannot  compete 
with  them  except  in  special  work  for  which  they  are  most  used. 


HAMMER   DRILLS 


55 


Kimber  Air-Hammer  Drill.  —  The  Kimber  drill,  Fig.  49,  and 
the  Gordon  drill,  Fig.  50,  were  designed  to  meet  certain  special 
conditions  largely  peculiar  to  the  district  of  the  Witwatersrand 
in  South  Africa.  The  Kimber  drill  is  merely  in  its  experimental 
stages,  so  I  merely  give  a  drawing  and  brief  description. 

The  Kimber  drill  with  a  cylinder  diameter  of  3|  in.,  length  of 
stroke  3  in.,  length  of  feed  1  in.,  weighs  100  Ib.  The  hammer  or 
striker  is  actuated  without  a  valve  on  the  differential  piston  prin- 
ciple, striking  800  to  1000  blows  per  minute.  The  weight  of  the 
hammer  is  12  Ib. 

The  rotation  of  the  drill  steel  is  effected  by  a  small  cylinder 
cast  on  the  front  end  of  the  main  cylinder  and  at  right  angles  to 
it.  To  the  piston  of  this  cylinder  is  attached  a  pawl,  which 


FIG.  48.  —  Leyner  rock  terrier  drill. 


engages  with  a  ratchet  wheel.  This  ratchet  wheel  has  a  square 
hole  through  the  center  to  receive  the  chuck  on  which  the  blow 
is  struck.  The  square  part  of  this  chuck  is  made  a  sliding  fit 
and  is  allowed  to  move  longitudinally  as  the  blows  are  struck, 
while  the  ratchet  wheel  gives  the  turning  movement.  The  small 
piston  is  driven  forward  by  means  of  air,  admitted  to  one  end  and 
governed  by  ports  communicating  with  the  main  piston,  and  is 
driven  backward  by  a  spring.  The  arrangement  is  such  that 
for  each  blow  the  drill  steel  makes  -fa  of  a  revolution.  The 
cradle  is  cylindrical  in  shape,  with  a  slot  at  the  top,  which  fits 
a  lug  cast  on  the  cylinder  and  forms  a  slide.  The  feed  is  obtained 
by  means  of  a  screw  and  nut,  with  a  crank  handle  attached  in 
the  ordinary  way. 

These  drills  are  built  to  put  in  45-in.  holes  in  narrow,  flat 
stopes  in  hard  quart zite  where  most  of  the  holes  dip  10  to  45  deg. 


56 


ROCK  DRILLS 


HAMMER   DRILLS 


57 


8 


58  ROCK  DRILLS 

from   the   horizontal   and  where  it  is  necessary  to  mount  the 
machine  on  a  bar  and  arm. 

Gordon  Air-Hammer  Drill.  —  The  Kimber  machine  and  the 
Gordon  machine,  Fig.  50,  are  also  designed  to  work  with  air 
pressures  as  low  as  50  lb.,  which  explains  the  fact  that  the  Kimber 
machine  uses  a  12-lb.  hammer  with  3-in.  stroke  to  drive  much 
smaller  and  shorter  bits  than  those  used  in  the  Leyner  machine. 
This  also  explains  the  great  length  of  stroke  adopted  in  the 
Gordon  machine.  Both  machines  are  also  built  with  the  idea  of 
being  one-man  machines,  i.e.,  being  easily  handled  and  rapidly 
operated  by  one  man.  The  weight  of  the  Gordon  drill  has  been 
cut  down  to  about  72  lb.  The  hammer  of  the  Gordon  drill 
weighs  about  1J  lb.  and  has  a  diameter  of  1A  in.  So  far,  despite 
its  apparently  simple  construction,  this  machine  has  given  poor 
results  in  actual  work  owing  to  the  various  difficulties  involved 
in  its  construction.  It  was  a  mistake  to  employ  a  light  hammer 
with  such  a  high  velocity  due  to  long  stroke.  It  is  a  most  rapid 
driller  with  moderate  sized  bits  in  holes  about  42  inches  deep.  It 
uses  much  less  air  than  a  piston  drill.  It  is  designed  to  strike 
about  600  blows  per  minute  with  air  at  50  lb.  pressure.  As  with 
the  Leyner  machine,  this  high  drilling  efficiency  is  aided  greatly 
by  water  issuing  from  hollow  steel  at  the  cutting  edge,  removing 
rock  particles  as  broken.  The  water  is  introduced  in  the  front 
head  through  the  anvil  block  or  striking  piece. 

HAND  HAMMER  DRILLS 

The  hammer  drill  was  used  first  as  a  hand  drill  for  cutting 
small  holes  for  hitches  or  pop  holes  in  large  rocks.  These  drills 
weigh  18  to  25  lb. 

"Hardy  Simplex.  —  The  Hardy  simplex  hammer  drill  weighs 
28  lb.,  and  can  drill  holes  6  to  7  ft.  deep.  The  arrangement  of 
piston  and  valve  can  be  gathered  from  Figs.  52  and  53.  It  con- 
sists essentially  of  a  cylinder  in  which  is  caused  to  reciprocate  by 
compressed  air  a  hardened  steel  hammer  or  piston  which  strikes 
on  the  drilling  tool  1500  to  2000  times  a  minute;  moreover, 
the  borer  is  turned  automatically. 

Cleveland  Hammer  Drills.  —  The  makers  of  Cleveland  drills 
claim  the  following  advantages  for  the  valve  hammer  drills :  They 
are  all  of  the  valve  type,  the  valve  being  the  same  in  design  as 
is  at  present  in  use  in  over  25,000  Cleveland  riveters  and  chippers. 


HAMMER   DRILLS 


59 


They  contend  there  is  no  question  about  the  superiority  of 
the  valve  over  the  valveless  type  of  drills  in  innumerable  ways. 


FIGS.  51  and  52.  —  Details  of  the  Hardy-Simplex  hammer  drill. 

And  they  also  state  that  with  the  valve  drill  assured  of  equal 
distribution  of  air,  which  minimizes  the  wear  of  both  piston  and 


Haw 


FIG.  53.  —  The  patent  Hardy-Simplex  hammer  drill. 

cylinder,   a  heavier  blow  is  delivered  since  the  piston  is  driven 
forward  against  atmospheric  pressure  only,  the  initial  air  pres- 


60 


ROCK    DRILLS 


sure  behind  it  being  maintained  throughout  the  stroke.  The  pis- 
ton is  solid  tool  steel  and  practically  unbreakable.  Less  than  70 
per  cent,  of  the  air  is  required  to  do  the  same  amount  of  work, 


FIG.  54.  —  Cleveland  hammer  drill. 

which  means  quite  a  saving  of  money  in  a  year's  time;  there  is 
less  vibration  to  the  machine,  and  it  is,  therefore,  much  easier  to 
hold  when  operating  by  hand,  and  the  parts  have  less  tendency 
to  crystallize.  Variations  in  air  pressure  have  little  or  no  effect 


FIG.  55.  —  Sullivan  hand  hammer  drill,  D — 15. 

on  their  operation,  while  a  valveless  drill  must  have  constant 
high  pressure.  Weight  20  Ib.  The  drill  is  shown  in  section  in 
Fig.  54. 

Sullivan  Hammer  Drill.  —  The  "D  15"  is  also  used  for  holes 


HAMMER   DRILLS 


61 


up  to  30  inches  in  depth,  and  together  with  the  "D  19"  machine, 
which  has  a  capacity  of  from  1  to  4  ft.,  for  drilling  pop  or  block 
holes,  for  splitting  up  large  boulders  or  pieces  of  stone  in  lime 
rock,  cement  rock,  and  trap  rock  quarries,  and  in  open-cut 
contract  work,  to  render  these  blocks  small  enough  to  be  handled 
by  the  excavator.  For  this  work  hollow  steel  is  ordinarily  em- 
ployed, the  entire  drill  being  rotated  by  means  of  a  handle.  See 
Fig.  55  for  sectional  view. 


TABLE  OF  SIZES  AND  WEIGHTS  OF  SULLIVAN  Am  HAMMER  DRILLS 


Class  of  Drill 

D15 

D  19 

D  21 

Diameter  of  cylinder  (inches)  
Depth  to  which  holes  may  be  drilled  (inches)  
Maximum  diameter  of  holes  (inches)  . 

Hf 

6  to  30 
H 

U 
12  to  48 
If 

2 
96 
2 

Size  of  hose  recjiiired  (inches) 

T?(5 

i 

i 

Air  consumption  at  100  Ib.  pressure  cu.  ft.  per  min  . 
Weight  of  drill  in  pounds  . 

15 

18 

25 
30 

35 
70 

Sinclair  Valveless  Hand  Drill.  —  This  machine,  Fig.  56,  is 
particularly  adapted  to  shaft  and  wing  work, 
cutting  hitches,  taking  up  bottoms  of  drifts, 
underhand  stoping  and  block-holing.  The 
construction  is  such  that  the  handle  can  be 
removed  and  the  feed  bar  attached  when 
desired.  One  10  X  12-inch  compressor  will 
operate  five  or  six  drills. 

Murphy  Standard  Drill.  —  The  accom- 
panying cut,  Fig.  57,  represents  the  No.  1 
or  standard  machine  with  handle,  and  Fig.  58 
shows  a  section  of  the  machine  and  parts. 
This  machine  weighs  17J  Ibs.  It  can  be 
used  to  good  advantage  as  a  hand  machine 
in  all  kinds  cf  work.  There  is  only  one 
moving  part,  to  wit,  the  hammer.  The  drill 
steel  is  hollow  and  part  of  the  exhaust  air  passes  through  it  and 
blows  back  the  cuttings  from  in  front  of  the  bit. 

The  drill  is  operated  by  one  hand  grasping  the  handle  and  the 
other  the  throttle  valve.     The  drill  is  rotated  back  and  forth 


FIG.   56.  —  Sullivan 
valve  hand  drill. 


62 


ROCK  DRILLS 


one-fourth  the  way  around,  with  the  hand  grasping  the  throttle 
valve.  The  machine  strikes  2000  blows  a  minute, 
and  requires  30  cu.  ft.  of  air  per  minute. 

Hardscogg  Little  Wonder.  —  The  "  Little  Won- 
der" trigger  valve  drill,  Fig.  59,  is  especially 
adapted  for  block-holes,  hitch  cutting  and  in  all 
work  where  it  is  necessary  to  start  and  stop  the 
drill,  at  frequent  intervals.  The  air  is  admitted 
to  the  drill  by  a  valve  operated  and  controlled 
by  the  finger,  and  so  constructed  that  it  will 
remain  open  when  desired,  but  can  be  instantly 
closed.  Weight  19  Ib. 


It 


HOLLOW  DRILL  STEEL 
was,    however,    only    when    the    air-feed 


stoping  bar  was  introduced  that  the  present 
heavier  types  of  hammer  drills  were  developed. 
This  development  was  also  helped  by  the  use  of 
hollow  steel.  Hollow  steel  of  good  quality  at  a 
reasonable  price  has  been  produced  the  last  few 


with   handle,  sinking  or  in  drifting,  a  portion  of  the  exhaust 

Carnahan  Mfg.   ajr  an(j  some  }jve  air  is  passed  through  the  hollow 

steel  to  the  bottom  of  the  hole  and  thus  removes 

the  broken  rock  chips.     It  must  be  remembered  that  for  drilling 

down-holes  with   hammer   drills,   hollow  steel  with  air,  air  and 

water,  or  water  alone,  under  pressure,  must  be  used  to  remove 


FIG.  59.  —  Hardscogg's  No.  2,  wonder  drill  with  trigger  valve. 


the    drillings,  as    there    is    not    the    splash  and  spitting  action 
caused  by  the  stroke  of  piston  drills. 


HAMMER   DRILLS 


63 


64  ROCK  DRILLS 

The  Leyner  people  claim  that  drilling  is  more  rapid  with  only 
air  passing  down  the  steel,  than  with  air  and  water.  This  is 
due  to  the  fact  that  the  particles  of  cut  rock  are  more  mobile  with 
an  air  blast  than  when  in  a  state  of  mud,  and  so  are  more  rapidly 
driven  out  of  the  way  of  the  cutting  edges.  The  water,  though, 
preserves  the  temper  of  the  bit  and  allays  the  dust  trouble. 

HAMMER  DRILL  USED  ON  STOPING  BAR 

The  hammer  drill  of  to-day,  with  air  feed,  as  a  practical  ma- 
chine, is  employed  mainly  for  holes  having  a  high  elevation  out 
of  which  the  cuttings  fall  by  gravity.  Solid  steel  is  used.  In 
most  places  where  the  practice  is  not  prohibited  by  law  the  miners 
have  to  put  up  with  the  dust  produced.  In  the  St.  John  del 
Rey  mine,  Minas  Geraes,  Brazil,  the  management  has  provided 
masks  for  their  workmen. 

This  type  of  hammer  drill  was  developed  in  the  Cripple  Creek 
mines  of  America.  The  conditions  that  called  it  into  being  were 
fairly  hard  ground;  expensive  labor,  narrow,  steeply  inclined 
stopes  carrying  rich  ore,  that,  owing  to  high  transportation  and 
treatment  charges,  must  be  mined  with  the  minimum  of  waste 
rock.  It  was  impossible  to  use  large  machines,  although  2J-in. 
piston  drills  were  formerly  employed  to  put  in  5-ft.  holes.  These 
drills,  weighing  up  to  134  lb.,  were  heavy  handling  for  one  man, 
and  required  to  be  firmly  set  up  on  a  bar.  The  clamp  bolts  had 
to  be  loosened  whenever  a  change  of  steel  was  made  or  a  new  hole 
started.  The  hammer  drill  with  stoping  bar  changed  all  this. 

Sloping  Bar.  —  The  bar  'consists  of  a  piston  which  forms  the 
extension  of  the  machine  proper,  instead  of  a  handle.  This 
piston  works  in  a  long  pipe-like  cylinder  with  packing  rings  to 
prevent  air  leakage.  At  the  base  of  the  cylinder  is  a  cock  for 
the  admission  of  compressed  air,  and  also  a  spike  to  fix  against 
the  rock  or  a  plank.  The  machines  are  rotated  or  oscillated  by 
hand.  With  hose  and  stoping  bar  they  are  light  and  easily  carried 
by  one  man.  They  are  taken  into  the  stope.  The  spike  of  the 
stoping  bar  is  fixed  on  a  board  on  the  broken  rock  or  on  a  timber; 
a  short  drill  is  fitted  into  the  chuck  and  placed  where  the  hole  is 
required.  The  air  is  turned  on  and  the  piston  of  the  stope-bar 
automatically  clamps  everything  in  position  and  drilling  begins. 
When  the  first  drill  is  run  out  the  air  is  turned  off  behind  the 
stope-bar  piston;  the  machine  is  run  back,  a  new  drill  inserted, 


HAMMER  DRILLS  65 

the  air  turned  on  again  and  drilling  proceeds.  Thus  very  little 
time  is  lost  as  one  man  can  actually  drill  from  80  to  90  per 
cent,  of  his  total  working  time,  against  perhaps  50  per  cent,  with 
a  piston  drill.  Wolcott  says  "a  2-in.  hammer-drill  drills  40  ft. 
in  8  hours  against  25  ft.  for  a  2|-in.  piston-drill,  in  Cripple  Creek 
granite."  In  drilling,  these  machines  are  generally  mounted  on 
a  2J-in.  column  with  arm  and  bar.  Hollow  steel  is  used  with 
air  or  air  and  water;  this  manipulation  thus  takes  more  time. 
The  length  of  hole  put  in  by  2-in.  hammer  drills  is  from  4  to  6 
ft.,  the  hole  being  usually  1  in.  in  diameter  at  bottom. 

Hammer  Drills  in  Europe.  —  In  Europe,  especially,  hammer 
drills  are  coming  into  extended  use  for  coal  mining,  working 
splendidly  in  coal  and  the  soft  formations  of  sandstone,  limestone, 
slate,  etc.,  associated  with  it.  In  mining  metalliferous  ores  and 
in  quarries  the  smaller  sizes  save  much  time  in  " popping,"  " bull- 
dozing," and  "  block  holing,"  to  break  up  large  boulders  of  ores 
displaced  by  heavy  changes  of  explosives. 

TYPES  OF  HAMMER  DRILLS 

Most  hammer  drills  are  made  to  operate  with  compressed 
air  at  80  to  100  Ib.  pressure.  The  following  are  illustrations 
and  short  descriptions  of  the  principal  makes:  Stephens  Imperial 
hammer  drills,  Sinclair  air-feed  drill,  Murphy  drill,  Sullivan  air- 
hammer  sloping  drill,  Hardscogg  Wonder  air-hammer  drill,  Cleve- 
land stope  drill,  and  the  Waugh  drifting  and  sinking  drills. 

The  Stephens  Climax  Imperial  Hammer  Drill.  —  An  English 
firm,  R.  Stephens  &  Son,  of  Cornwall,  has  designed  a  hammer 
drill  built  as  largely  as  possible  on  the  lines  of  a  piston  drill  and 
having  every  part  readily  accessible  for  inspection;  this  is  the 
latest  type  of  hammer  drill,  especially  designed  to  meet  the  con- 
ditions on  the  Rand.  In  designing  this  drill,  it  was  determined 
to  construct  a  machine  of  the  maximum  power  possible  within 
the  limiting  weight  of  100  Ib.  laid  down  as  the  maximum  weight 
allowed  for  machines  competing  for  the  £4000  prize  on  the  stope- 
drill  contest.  In  this  drill  air  consumption  has  not  'been  con- 
sidered an  important  item.  The  consumption  is  given  as  being 
about  three-fifths  that  of  a  3j-in.  drill.  It  would  therefore 
be  about  equal  to  that  of  a  2f-in.  drill  or  from  70  to  80  cu. 
ft.  per  minute  with  air  at  a  pressure  of  80  Ib.  per  square  inch. 
The  complete  machine  weighs  95  Ib.,  20  Ib.  more  than  the 


66 


ROCK  DRILLS 


Gordon  drill.  With  an  air  pres- 
sure of  75  Ib.  per  square  inch,  the 
number  of  strokes  per  minute  is 
said  to  be  about  700. 

The  length  of  stroke  is  5  in. ; 
the  diameter  of  cylinder  is  If  in., 
and  the  weight  of  the  hammer  is 
6f  Ib.  It  will  be  seen  that  this 
drill  is  more  powerful  than  any 
American  stoping  drill  except  the 
Leyner,  model  6  machine.  The 
general  construction  of  the  ma- 
chine which  includes  some  novel 
features  can  be  seen  from  the 
accompanying  sketch  sections. 
Fig.  60,  part  1,  is  a  longitudinal 
section;  part  2  is  a  transverse 
section.  Fig.  61  shows  the  ma- 
chine set  up  for  work  and  also 
two  drill  bits.  In  Fig.  60  A  is 
the  anvil  block.  It  is  about  9 
in.  long  by  If  in.  diameter;  it 
weighs  8  to  10  Ib.  The  anvil 
block  and  pinion  wheel  G  are 
made  in.  one  piece  and  from 
special  steel.  This  pinion  wheel 
prevents  the  anvil  block's  being 
forced  back  into  the  cylinder. 
It  will  be  noted  that  it  is  pro- 
vided with  a  taper  recess  for  a 
taper  chuck  C,  having  a  water- 
feed  channel  WFC  through  it. 
This  channel  communicates  with 
a  brass  water-feed  ring  W,  which 
is  surrounded  by  buffer  rings 
made  water-tight  by  packing  PK. 
Water  is  fed  from  the  two-way 
throttle  valve,  shown  in  the  half- 
tone illustration,  through  the 
channel  WFC,  along  the  side  of 
cylinder  and  front  head  to  the 
brass  water  ring  W. 


HAMMER  DRILLS  67 

The  amount  of  water  used  is  regulated  by  means  of  two  cocks 
—  one  on  the  hose;  the  other,  a  brass  screw-head,  on  the  machine 
itself.  No  air  passes  down  the  hollow  steel  with  the  water.  Any 
water  leaking  past  the  ring  toward  the  cylinder  drains  away 
through  holes  ES  W. 

The  pinion  wheel  S  gears  with  the  spur  wheel  G]  this  is  ro- 
tated by  crank  handles  to  which  it  is  connected  by  a  telescopic 
rod.  The  rotation  is  thus  geared  and  positive,  being  operated 
by  hand  similarly  to  the  way  that  rotation  is  effected  in  the 
Leyner  "Rock  Terrier"  drill,  which  this  machine  resembles  some- 
what. FF  is  the  main  cylinder  casting  and  slides  in  the  flat 


FIG.  61.  —  Stephens  Climax  Imperial  hammer  drill. 

cradle.  It  is  bored  out  for  two  cylinders;  AFC  is  the  air-feed 
cylinder,  AFP  is  the  air-feed  piston  attached  to-  the  cradle. 
The  air  admitted  to  the  machine  enters  the  air-feed  cylinder  and 
feeds  the  machine  forward  before  it  enters  the  main  cylinder; 
as  soon  as  the  air  is  turned  off,  AFC  is  opened  so  as  to  exhaust. 
The  drill  must  be  slid  back  by  hand,  but  as  the  drill  is  light  and 
the  holes  seldom  vertical  this  can  be  easily  done.  Another  for- 
ward feed  is  gained  (see  Fig.  61)  by  sliding  the  cradle  forward 
in  the  clamp.  One  side  of  the  cradle  has  teeth  on  it;  when  the 
clamp  bolt  is  loosened  the  cradle  slides  easily  forward  and  is  then 
securely  fastened  again  by  the  toothed  clamp,  when  it  is  tightened. 
With  these  two  feeds,  a  total  advance  of  28  inches  is  gained; 


68  ROCK   DRILLS 

this  is  ample  in  the  hard  ground  here,  where  hammer-drill  bits 
are  generally  blunted  after  boring  12  or  15  inches. 

The  main  cylinder  is  If  in.  in  diameter.  The  piston  P  is  of 
shape  shown.  PO  and  PO'  are  the  air  ports;  VB  is  the  valve 
chest;  V  is  a  piston  valve,  and  AV  and  AV  are  two  auxiliary 
leather  valves  which  control  the  exhaust  from  the  valve  ends. 
They  are  pushed  down  so  as  to  always  make  an  air-tight  sliding 
fit  with  the  piston  P,  no  matter  how  worn  the  cylinder  may  be. 
Thus  the  valve  movement  is  kept  regular. 

The  valve  action  can  be  seen  from  Fig.  60.  The  air  is  allowed 
to  leak  past  each  end  of  the  valve  from  the  live-air  chamber  in 
the  center  of  the  air  chest  in  sufficient  quantity  to  throw  the  valve 
over  when  the  other  end  is  open  to  exhaust.  The  movements  of  the 
piston  P  place  each  end  of  the  valve  chest  alternately  in  connection 
with  the  atmosphere  through  AV  and  AV,  the  recess  in  piston 
and  the  two  exhaust  ports  EX  and  EX'  in  the  walls  of  the  cylin- 
der. In  Fig.  60  the  piston  P  has  finished  its  stroke,  and  A  V  is 
open  to  exhaust,  so  the  valve  will  be  thrown  over  for  the  return 
stroke.  The  valve  could  be  set  to  cut  off  and  use  air  expansively 
on  either  front  or  return  stroke.  This  is  done  in  the  large  piston 
drill  made  by  the  same  company.  It  will  be  noted  that  the 
valve  motion  is  simple  and  that  the  valve  can  be  easily  inspected. 
The  machine  is  held  together  by  side  rods  SR.  The  packing 
in  the  front  head  can  be  readily  taken  out  and  changed  if  it 
becomes  worn. 

The  novel  points  about  the  design  are:  First,  the  compact 
air  feed  which  allows  the  machine's  being  kept  short  and  so  made 
similar  in  shape  to  a  piston  drill,  and  yet  without  a  feed-screw; 
second,  the  great  weight  of  the  anvil  block  —  this  would  seem  at 
first  to  be  a  mistake  in  design  owing  to  its  great  weight  and 
inertia;  third,  the  adoption  of  the  taper  chuck  attachment. 
This  makes  the  anvil  block  simply  a  part  of  the  drill  bit  as  it 
fastens  immediately  to  the  drill  shank.  This  construction  seems 
to  me  to  reduce  vibration  greatly  and  to  be  the  reason  why  the 
makers  say  that  they  have  had  no  trouble  with  breakages  of  this 
part,  in  spite  of  the  fact  that  it  has  holes  bored  in  it  and  of  the 
difficulty  that  every  maker  finds  in  tempering  anvil  blocks  with 
holes  in  them.  The  anvil  block  is  always  "up  to  its  work,"  and 
there  is  never  any  lost  motion  between  it  and  the  drill  owing  to 
rebound.  Of  course,  a  somewhat  harder  blow  has  to  be  struck 


HAMMER   DRILLS  69 

to  make  up  for  the  greater  inertia  of  the  combined  boring  tool, 
but  the  advantage  gained  seems  to  outweigh  this. 

The  machine  does  not  seem  to  be  very  economical  in  air,  for 
the  cylinder  volume  on  the  return  stroke  is  large,  owing  to  the 
fact  that  there  is  no  piston  rod  to  take  up  this  space.  The  length 
of  the  machine  over  all  is  2  ft.  10  in. 

I  witnessed  a  trial  of  this  machine  on  a  block  of  granite  similar 
to  that  used  in  the  South  African  mines  stope-drill  competition. 
The  hole  drilled  was  horizontal,  the  water  pressure  about  10  lbv 
and  the  air  pressure  80  Ib.  per  square  inch.  The  machine  bored 
about  12  in.  with  a  IJ-in.  double-chisel  bit,  13  in.  with  a  IJ-in. 
chisel  bit,  and  14  in.  with  a  1-in.  chisel  bit;  or  a  total  of  39  in.,  in 
a  total  of  9  min.  22  sec.,  or  an  actual  drilling  time  of  8  min.  48 
sec.  The  average  speed  was  4.23  in.  per  minute. 

In  another  trial  36|  in.  was  bored  in  12  min.  15  sec.;  the  bits 
were  chipped  and  well  blunted.  It  will  be  noted  that  the  width 
of  the  bits  used  was  less  than  that  of  those  used  in  the  South 
African  mines  trials;  had  the  drilling  been  done  with  1J-,  1J-, 
and  If-in.  bits,  the  rate  of  drilling  would  be  slower.  In  the  Gov- 
ernment trials  in  1909  the  finishing  gage  of  the  holes  at  a  depth 
of  48  in.  was  If  in.  This  meant  that  holes  would  have  to  be 
started  with  If-  or  IJ-in.  bits.  I  have  already  shown  what  effect 
this  has  on  boring  speed.  This  machine,  I  should  say,  has  a  speed 
of  boring  equal  to  that  of  2|-in.  piston  drill  having  a  6-in.  stroke 
and  boring  with  bits  of  the  same  size;  but  the  Stephens  is,  of 
course,  lighter,  smaller  and  more  easily  handled  than  the  piston 
drill,  while  with  a  double-pointed  wedge  key  the  drill  bits  are 
changed  very  rapidly  indeed.  The  shape  of  drill  bits  used  is 
shown  in  Fig.  61.  The  shank  ring  is  necessary  for  taking  out 
the  bits  by  means  of  the  key. 

Sinclair  Hammer  Drill.  —  The  advantages  claimed  for  this 
drill,  Fig.  62,  are: 

1.  It  has  been  the  endeavor  of  its  inventors,  by  employing 
machine  and  tool  steel  in  the  place  of  cast  iron,  to  build  a  machine 
which  is  practically  indestructible.     It  is  constructed  of  machine 
and  tool  steel  throughout,  except  the  throttle  valve,  which  is  of 
polished  brass. 

2.  It  is  simple   and   substantial.     An  endeavor  has  been  to 
make  the  machine  so  simple  and  strong  in  every  particular  that 
there  is  little  or  no  chance  for  leakage. 


70  ROCK  DRILLS 

3.  It  is  protected  against  crystallization  by  buffers  and  buffer 
plates.     One  of  the  faults  noticed  in  hammer  drills  is  the  tendency 
toward  crystallization  of  the  steel  in  the  cylinders.     This  is  caused 
by  the  piston  striking  the  chuck,  or  collar  protecting  the  chuck, 
when  the  steel  is  not  far  enough  into  the  machine  to  allow  the 
piston  to  ^strike  the  end.     In  the   Sinclair   drill   this    defect   is 
entirely  obviated  by  f-in.  rubber  buffers  and  steel  buffer  plates. 

4.  Steel  used  is  either  hollow  or  solid,  with  no  bulldozed  shanks 
to  break  and  cause  trouble.     A  bulldozed  shank  is  not  required 
as  the  shoulder  necessary  to  keep  the  steel  from  going  far  into 
the  chuck  is  made  by  turning  off  the  shank  end  of  the  drill  steel. 
In  making  shanks  in  a  bulldozer,  the  hole  through  the  steel  is 
made  considerably  smaller  at  the  point  where  the  shoulder  is 


FIG.  62.  —  Sinclair  air-feed  drill. 

raised,  and  four  times  out  of  five  a  weak  place  is  made  where 
wreakage  will  occur. 

Murphy  Drill.  —  The  makers  thus  describe  the  No.  2  drill, 
Fig.  63,  with  water  attachment  and  air  feed,  as  follows: 

In  up-raises  and  stopes,  where  up-holes  only  are  required, 
solid  steel  is  generally  used  with  the  Murphy  drills.  In  shaft 
sinking  and  all  down-hole  work,  hollow  steel  is  used  and  water 
added  in  the  usual  manner,  but  in  drifting,  or  in  any  work  in  a 
vertical  face,  it  is  necessary  to  put  in  up-holes,  down-holes,  and 
horizontal  holes,  and  in  such  work  hollow  steel  is  required,  and 
it  is  not  convenient  to  add  water  in  the  usual  manner.  In  such 
work  the  Murphy  No.  2  machine,  with  feeder  mounted  on  column, 
is  usually  used,  and  this  is  provided  with  the  water  attachment 
as  shown  in  the  illustration.  The  tank  is  light,  is  provided  with 
handles,  and  is  easily  moved  about.  Compressed  air  is  admitted 
above  the  water  in  the  tank.  A  50-ft.  length  of  f-in.  hose  is  con- 
nected to  the  water  in  the  tank  and  to  the  side  of  the  Murphy 


HAMMER  DRILLS 


71 


FIG.  63.  —  Murphy  No.  2  drill  wit] 


iment. 


ROCK  DRILLS 


FIG.  64.  —  Sullivan  D-21  air  hammer  drill. 


HAMMER  DRILLS 

drill.  Water  is  forced  through  the  hollow  steel. 
A  needle  valve  is  on  the  water  line,  so  that  it 
may  be  regulated  just  as  required.  A  small 
amount  of  water  only  is  needed.  A  tank  full 
should  last  a  shift.  A  small  piece  of  sponge 
is  put  in  the  hose  connection,  so  that  it  is 
necessary  for  the  water  to  strain  through  this 
sponge  before  reaching  the  needle  valve.  This 
is  done  to  prevent  any  solid  particles  getting 
to  the  needle  valve  and  clogging  it.  If  the 
sponge  clogs  it  can  be  quickly  removed, 
washed  out,  and  replaced. 

The  Sullivzn  Air-Hammer  Drill.  —  The  Sul- 
livan Class  "D  21,"  Fig.  64,  mining  drill  is  de- 
signed for  driving  stopes  and  raises.  It  is 
mounted  on  a  feed  cylinder  and  piston,  the 
rear  end  of  which  rests  upon  the  floor  or  back 
wall  of  the  working.  As  the  drill  bit  advances 
the  feed  piston  is  also  advanced  by  compressed 
air,  thus  automatically  keeping  the  drill  up  to 
its  work.  The  machine,  complete,  weighs  70  Ib. 
and  employs  solid  steel.  As  the  holes  are  all 
uppers  they  are  kept  free  of  the  cuttings  by 
gravity.  The  drill  is  rotated  by  hand  and  will 
put  in  holes  up  to  6  ft.  in  depth.  It  uses  only 
a  small  quantity  of  air  as  compared  with  the 
standard  piston  drill,  and  owing  to  its  light 
weight  and  absence  of  separate  mounting  may 
be  carried  readily  and  quickly  into  any  working 
where  a  man  may  go,  and  may  be  set  up  and 
removed  more  rapidly  than  a  machine  mounted 
on  a  tripod  or  column. 

Hardscogg  Wonder  Air-Feed  Water  Drill  - 
In  some  formations  where  the  rock  is  exceed- 
ingly dry  and  free  cutting,  the  dust  from  a  drill 
giving  an  air-cleaned  hole  is  objectionable.  To 
overcome  this  a  special  machine,  Fig.  65,  has 
been  built,  with  a  water  device,  with  which 
water  is  used  rather  than  air  to  expel  the  drill 
cuttings.  The  water  is  taken  into  the  drill 


74 


ROCK  DRILLS 


HAMMER  DRILLS 


75 


and  passes  into  the  end  of  the  drill  bit.  This  arrangement  also 
obviates  the  necessity  of  using  a  special  water  socket  or  water 
joint.  Water  may  be  taken  from  a  water  pipe  or  column,  or 
from  a  special  water  tank,  as  desired.  The  drill  is  simple  in 
construction  and  there  are  no  complicated  or  expensive  parts 
liable  to  break  or  get  out  of  repair.  With  this  device  the  drill 
and  bit  are  completely  rotated,  which  assures  a  perfectly  round, 
smooth  hole  and  prevents  the  drill  bit  from  sticking. 

It  is  recommended  and  guaranteed  to  drill  a  4-ft.  hole,  and  its 
weight  complete,  with  6-ft.  column  and  arm,  is  100  Ib. 

Cleveland  Slope  Drill.  —  The  drawing,  Fig.  66,  shows  the 
design  of  the  Cleveland  stope  drill.  The  valve  chest  being  on 
the  outside,  renders  the  valve  easily  removed  without  disturbing 
any  other  part  of  the  machine,  in  case  it  sticks,  because  of  dirt  in 


FIG.  67.  —  Cleveland  hammer  drill  and  air  feed 

the  air  line;  and  inasmuch  as  the  chuck,  back  head,  and  cylinder 
are  held  together  by  side  rods  the  whole  machine  can  be  pulled 
apart  in  a  few  minutes,  should  this  operation  be  necessary.  This 
drill  can  be  entirely  taken  apart  and  assembled  again  in  the  mine, 
without  using  a  vise,  and  without  taking  the  drill  on  top.  The 
operation  of  the  machine  is  simple,  and  as  follows : 

After  the  machine,  Fig.  67,  is  set  in  place  and  the  air  line  con- 
nected, the  throttle  handle  being  in  line  with  the  machine,  a  turn 
to  the  first  notch  opens  the  air  feed  enough  to  slowly  raise  the  drill 
to  the  rock;  the  next  notch  starts  the  hammer  running  slowly, 
and  the  last  starts  the  hammer  at  full  speed.  It  is  then  only 
necessary  to  keep  the  drill  rotating  back  and  forth  through  180° 
until  the  air  is  shut  off,  in  order  to  keep  the  holes  round  and  in 
shape  to  receive  the  next  steel.  Closing  the  throttle  opens  a 
small  relief  hole,  allowing  the  air  feed  to  telescope.  To  get  the 
greatest  possible  amount  of  drilling  out  of  the  machine,  the  air 


76  ROCK   DRILLS  * 

pressure  at  the  drill  should  be  between  80  and  100  Ib.     The  air 
consumption  at  this  pressure  is  about  35  cu.  ft.  per  minute. 

If  the  machine  is  idle  a  long  time,  a  good  supply  of  oil  poured 
in  the  oilers,  and  the  machine  run  for  a  few  minutes,  will  clean  it 
out  thoroughly,  after  which  lubricating  oil  should  be  added.  Good 
oil  which  will  not  gum  must  be  used.  It  is  advisable  to  pour  a 
small  quantity  of  oil,  about  four  times  per  shift,  into  the  oiler  — 
the  action  of  the  machine  will  distribute  it  to  every  working  part. 
This  drill  uses  1-in.  cruciform  solid  steel  and  is  designed  to  put 
in  up-holes  only. 

Waugh  Drifting  and  Sloping  Drill.  —  The  Denver  Rock  and 
Machine  Company  says  that  a  special  feature  of  the  No.  8-D 
and  3-D  sinking  and  drifting  drills,  Fig.  68,  is  the  automatic 
tappet,  which  regulates  the  pressure  in  the  air-feed  cylinder,  so 
that  the  drill  will  always  rotate  easily.  The  duty  of  the  air-feed 
cylinder  is  to  keep  the  drill  steel  always  up  against  the  bottom 
of  the  hole,  and  owing  to  constant  pressure  expands  as  the  depth 
of  the  hole  is  increased.  An  air-feed  cylinder  with  sufficient  area 
to  keep  the  drill  and  steel  up  against  the  bottom  of  the  hole  when 
drilling  a  hole  above  the  horizontal  would  be  found  altogether 
too  powerful  on  a  down-hole,  when  in  addition  to  the  pressure 
in  the  air-feed  cylinder  is  added  the  weight  of  the  machine  and 
drill  steel. 

A  brief  explanation  of  the  working  of  this  automatic  tappet 
or  regulator  is  this :  There  are  two  annular  grooves  one  inch  apart 
around  the  small  end  of  the  tappet.  These  grooves  register  with 
ports  in  the  wall  of  the  barrel  which  connect  with  the  air  supply 
in  the  air-feed  cylinder,  and  automatically  regulate  the  pressure 
in  the  air-feed  cylinder  according  to  the  hardness  of  the  rock 
being  drilled.  This  alternating  pressure  is  obtained  by  the  shift- 
ing of  the  tappet,  which  change  in  position  is  caused  by  the  recoil 
of  the  piston  hammer.  In  drilling  in  hard  rock  this  recoil  is  more 
accentuated  than  when  drilling  in  softer  rock,  and  the  position 
of  the  tappet  is  governed  accordingly. 

Waugh  drifting  and  sinking  drills  use  hexagon  hollow  steel. 
The  No.  8-D  uses  1-in.  hexagon  hollow  steel,  and  the  No.  3-D 
uses  |-in.  hexagon  hollow  steel.  There  are  no  prepared  shanks 
necessary  further  than  to  smooth  off  the  ends  and  harden  them 
slightly. 

To  get  results  from  the  operation  of  the  Waugh  hammer  drill 


HAMMER   DRILLS 


77 


in  putting  in  down  angle  holes  it  is  necessary  to  keep  the  bottom 
of  the  hole  free  from  cuttings.  This  is  done  by  a  very  simple 
three-way  valve  device,  which  is  connected  to  the  drifting  and 
sinking  drills.  The  three-way  valve  seat  is  screwed  into  the  side 
of  the  head,  and  the  three-way  valve  is  operated  by  the  sleeve 
handle,  which  fits  over  the  rotating  handle,  and  as  the  operator 
rotates  the  drill  he  can  very  easily,  with  a  simple  turn  of  the 
wrist,  change  the  position  of  the  three-way, valve  and  force  either 
live  air  or  water  through  the  drill  steel. 


FIG.  68.  —  The  Waugh  drill. 

There  is  a  hexagon  leather  gasket  in  the  chuck  end  of  the  drilll 
which  by  pressure  from  behind  makes  a  tight  joint  around  the 
drill  steel  and  keeps  the  water  and  air  from  escaping  out  of  the 
chuck  end,  and  causes  them  to  be  forced  through  the  hollow  drill 
steel  to  the  bottom  of  the  holes.  This  gasket  can  be  quickly 
replaced  when  worn  out,  and  in  putting  in  a  new  gasket  it  is  neces- 
sary to  be  sure  that  the  hexagon  sides  of  the  gasket  are  in  line 
with  the  hexagon  side  of  the  chuck. 

Nothing  but  a  light  oil  should  be  used  for  oiling  this  drill ;  lard 
oil  is  recommended.  In  addition  to  pouring  some  oil  in  the  short 


78 


ROCK   DRILLS 


hose  air  connection,  it  is  well  to  pour  some  oil  down  the  chuck 
end,  in  order  to  keep  the  tappet  chamber  lubricated.  The  No. 
8-D  weighs  75  Ib.  and  uses  40  cu.  ft.  of  air  per  minute;  the  No.  3-D 
weighs  60  Ib.  and  uses  35  cu.  ft.  of  air  per  minute. 

At  a  recent  trial  in  black  syenite  in  No.  6  shaft  Vindicator 
Mine,  Colorado,  the  Waugh  machine,  8  C,  drilled  49  ft.  in  I? 
hours,  and  the  Shaw  machine,  10  A,  drilled  35  ft.  in  1J  hours. 

"ANVIL-BLOCK"   MACHINES   COMPARED   WITH  THOSE'  STRIKING 
THE  STEEL  DIRECT 

The  anvil-block  striking  pin,  or  tappet,  is  a  short  cylinder  of 
specially  hardened  steel  fitting  in  the  end  of  the  cylinder  and  kept 
from  entering  it  by  an  annular  projection. 
It  sometimes  takes  the  form  of  a  false 
chuck  seen  in  Fig.  69.  When  this  is  em- 
ployed there  is  no  need  to  forge  or  turn 
any  collar  in  front  of  the  shank  on  the 
drill  steel.  It  also  tends  to  prevent  leak- 
age of  air  from  the  front  end  of  drill, 
though  if  it  be  used  with  hollow  steel  a 
hole  must  be  bored  in  it  to  allow  air  to 
pass  down  the  drill.  The  anvil  block  also 
helps  to  keep  grit  out  of  the  cylinder. 
When  boring  up-holes  with  a  machine  not 
using  this  device  grit  is  very  liable  to  enter 
through  the  front  head  around  the  shank 
of  the  drill.  In  practice,  the  disadvan- 
tages of  this  device  are  that  its  elasticity 
and  inertia  must  be  overcome  by  the  blow 
of  the  hammer.  If  it  is  not  pressed  very 
tightly  against  the  drill  shank  the  force 

FIG.  69.  —  False  chuck  of  the  blow  will  be  greatly  reduced.     Under 

Machine  O^    ^^  the  Prolonged  hammering  if  the  anvil  block 

is  not  tempered  to  a  nicety  it  will  either 

break  or  burr  up,  sometimes  wedging  itself  in  its  place.  A  recent 
writer  in  the  Engineering  and  Mining  Journal  states  that  the 
benefit  of  a  vanadium  alloy  is  that  it  allows  a  solid  anvil  block 
being  tempered  properly  all  the  way  through.  The  form  of  the 
solid  anvil  block  is  shown  in  Fig.  70.  In  the  Gordon  drill  it  is 
weakened  by  having  holes  bored  in  it  to  transmit  water  to  the 


HAMMER   DRILLS 


79 


end  of  the  hollow  drill  shank.  This  liability  to  rupture  becomes 
much  increased.  The  piston  can  be  made  very  solid  and  strong. 
It  will  be  noted  that  the  valve  machines  usually  have  an  anvil 


FIG.  70.  —  Average    type   of    hammer   in  which 
vanadium  steel  is  employed. 

block,  which  is  necessary  in  order  to  reduce  air  leakage  on  return 
stroke,  while  the  valveless  drills  strike  the  steel  direct. 

Valveless  Drills.  —  The  operation  of  valveless  drills  is  plainly 
seen  in  the  drawing  and  description  of  the  action  of  the  Kimber, 
Fig.  49,  and  Hardscogg  Little  Wonder 
machine,  Fig.  59.  It  is  evident  that  in 
machines  of  this  type,  when  live  air  is  ad- 
mitted to  drive  the  piston  hammer  back, 
considerable  leakage  must  occur  around  the 
shank  and  through  the  hollow  of  the  steel. 
With  most  of  these  machines  the  forward 
stroke  is  made  by  air  under  expansion,  the 
air  supply  being  cut  off  before  the  piston 
has  completed  its  travel  and  struck  its  blow. 
The  action  is  similar  to  that  of  the  Adelaide 
piston  drill.  With  many  of  the  valve  ma- 
chines full,  air  is  kept  on  the  piston  until 
the  end  of  stroke.  The  blow  is  not  cush- 
ioned and  is  harder.  The  piston  hammer  of 
the  valveless  machine  has  passages  and  holes 
bored  in  it,  thus  being  more  liable  to  break. 
Fig.  71  shows  the  principle  upon  which  the 
valveless  machines  work.  As  shown,  the 
hammer  H  is  on  the  forward  stroke  and  the 
air  entering  at  /  passes  through  the  ports  P 
in  the  hammer  and  exerts  a  forward  pressure  FIG. 
over  the  entire  rear  portion.  At  the  same 
time  the  exhaust  E  has  allowed  the  escape 

of  the  compressed  air  from  the  previous  stroke,  and  the  inner 
ring  R,  which  is  a  part  of  the  barrel  B,  prevents  the  air  from  the 
inlet  from  going  to  the  front  of  the  hammer.  The  effective  air 


71.  —  Section   of 


80  ROCK  DRILLS 

pressure  then  is  the  pressure  on  the  rear  portion  of  the  hammer 
minus  a  backward  pressure  upon  the  shoulder  S.  As  the  hammer 
moves  forward  the  ports  P  are  closed  by  the  ring  R,  until  the 
ring  is  passed,  when  they  open  to  the  exhaust  E;  the  air  pressure 
then  is  upon  the  shoulder  S  and  moves  the  hammer  back. 

Collars  have  to  be  placed  in  the  drill  steel  to  allow  the  front 
head  to  press  against  it  and  thus  prevent  the  shank  of  drill  steel 
entering  the  cylinder  too  far,  preventing  the  proper  stroke.  These 
collars  are  either  turned  off  the  steel  or  swaged  up  on  it.  If 
turned  off,  the  area  struck  by  the  hammer  is  reduced  too  much 
and  the  shank  will  be  liable  to  burr  up  or  break  while  swaying 
a  collar,  or  appears  to  weaken  the  drill,  as  they  often  break  at 
this  place.  These  drawbacks  can  be  reduced  by  using  the  largest 
possible  section  of  steel.  This  section  is  determined  by  the 
minimum  diameter  necessary  at  the  bottom  of  the  hole  bored. 
In  all  these  discussions  of  advantages  and  disadvantages  of  vari- 
ous machines  and  various  types  of  the  same  machine  the  question 
of  the  class  of  labor  available  for  supervision  must  always  be 
taken  into  consideration.  On  the  Continent  skilled  labor  with 
technical  knowledge  is  able  to  get  very  fair  results  from  electrical 
drills.  Hammer  drills,  with  attachment  for  water  feed,  with 
hollow  steel  require  careful  and  skilful  operators.  On  a  mining 
field  like  the  Witwatersrand,  where  the  labor  is  mainly  unskilled 
and  where  many  white  supervisors  are  both  careless  and  untrained, 
many  devices  that  might  be  a  success  elsewhere  fail  altogether. 

As  a  general  rule  the  miner  hates  complications  of  any  kind. 
He  would  in  some  cases  refuse  to  make  a  success  of  a  machine 
because  its  use  involved  coupling  up  a  few  extra  hose  and  a  tank 
before  he  started  work.  Unfortunately,  it  is  no  real  excuse  for 
the  failure  of  a  device  or  machine  to  say  that  if  it  had  had  care- 
ful treatment  it  would  have  been  all  right;  because  any  machine 
for  underground  work  must  put  up  with  careless  treatment  and 
neglect.  Herein  lies  the  cause  of  the  failure  of  several  machines 
of  the  hammer  type. 

DESIGN  OF  HAMMER  DRILLS 

The  design  of  a  good  hammer  drill  should  include  provision 
for  taking  up  the  blow  of  the  hammer  on  the  front  head  without 
seriously  damaging  the  machine.  It  will  be  noted  in  some  de- 
signs that  this  is  well  done  by  means  of  springs  and  side  rods 


HAMMER   DRILLS  81 

as  in  a  piston  machine.  In  others  it  is  provided  for  by  rubber 
buffer  plates.  If  the  machine  is  of  the  valve  type,  the  valve 
being  very  rapid  in  motion  should,  if  possible,  take  up  its  own 
wear  or  allow  of  having  its  seat  bored  out  and  a  new  valve  fitted 
easily.  It  should  have  some  arrangement  to  prevent  grit  enter- 
ing. Above  all,  the  valve  should  be  easily  accessible  for  examina- 
tion as  is  the  valve  of  a  piston  machine.  The  water  service 
should  be  arranged  so  that  the  water  cannot  corrode  any  vital 
internal  part  of  the  machine,  or  enter  the  cylinder  or  valve  chest. 
Leakage  due  to  wear  must  be  easily  taken  up. 

The  weight  of  hammer  and  length  of  stroke  should  be  suitable 
to  the  pressure  of  air  under  which  the  machine  will  work,  giving 
a  blow  hard  enough  to  cut  the  rock  with  long  steel,  yet  not  power- 
ful enough  to  smash  anvil  blocks  or  steel.  If  anvil  blocks  are 
used,  they  should,  if  possible,  be  kept  solid  and  not  weakened  by 
holes  bored  in  them. 

Rotation  or  oscillation  for  up-holes  is  best  performed  by  hand 
in  those  types  for  use  with  air-feed  stoping  bar  with  solid  steel. 
Mechanical  rotation  is,  however,  perhaps  preferable  for  those 
machines  used  on  bars  and  arms.  A  secondary  hand  rotation 
should  be  available  also.  The  design  of  hammer  drills  is  in  an 
evolutionary  stage.  Special  material  is  being  called  into  use  for 
their  construction.  Vanadium  steel  is  found  most  suitable  for 
anvil  blocks.  They  produced  a  demand  for  hollow  steel  and 
for  a  hard,  acid- water  resisting  alloy. 

To  define  the  limits  of  the  economical  use  of  hammer  drills 
at  this  time,  as  against  piston  drills,  is  difficult.  For  very  large, 
deep  holes  the  piston  drill  has,  at  present,  nearly  the  whole  field. 
The  Leyner  drill  challenges  its  position  for  holes  of  moderate  size 
and  length,  such  as  are  usually  employed  in  development  work 
in  mining.  A  drill  like  the  Leyner,  however,  is  hampered  by 
requiring  the  use  of  water  under  pressure,  valuable  as  such  an 
auxiliary  is  from  a  health  standpoint. 

THE  ADVANTAGES  OF  THE  HAMMER  DRILL  1 

"The  hammer  drill  is  extremely  simple,  having  only  one,  or 
at  the  most  two,  moving  parts.  This  means  a  steady  reliability 
and  ease  of  up-keep  with  low  repair  costs. 

"Requiring  but  a  moment  to  change  steels  or  start  a  new 
1  Ingersoll-Sergeant  Catalogue. 


82  ROCK  DRILLS 

hole,  probably  70  to  90  per  cent,  of  the  work  paid  for  is  applied 
in  actual  drilling,  while  with  an  ordinary  piston  drill  usually 
not  more  than  two-thirds  and  often  less  than  half  the  time  is 
actual  drilling  time.  This  is  a  most  important  point  in  work 
where  a  large  number  of  small,  shallow,  and  carefully  placed  holes 
are  required. 

"The  great  number  of  light  blows  of  the  hammer  drill  is  less 
destructive  of  steels  than  the  heavier  blow  of  the  piston  drill. 
The  loss  of  gage  of  the  bits  is  not  so  rapid.  The  breaking  or 
dulling  of  steels  for  a  given  footage  of  holes  is  much  less  than 
in  hand  drilling  and  usually  not  more  than  half  with  the  hammer 
drill  what  it  is  with  the  piston  drill. 

"The  hammer  drill  can  be  used  in  extremely  close  quarters 
—  places  where  no  piston  drill  with  a  fixed  mounting  could  be 
used,  or  even  a  hand  hammer  swung.  Wherever  a  man  can  go 
he  can  take  a  hammer  drill  with  him.  It  is  truly  a  'handy' 
machine,  easily  carried  anywhere  under  all  conditions. 

"The  air  consumption  of  hammer  drills  is  about  one-half 
that  of  the  smallest  piston  drill,  meaning  that  a  given  compressor 
plant  will  run  twice  as  many  hammer  drills,  doing  probably  twice 
the  work  and  often  more,  in  certain  conditions.  Or,  the  initial 
power  and  plant  investment  for  a  hammer  drill  outfit  to  do  a 
given  work,  as  in  prospecting  or  development,  need  be  much  less 
than  that  required  for  an  equipment  of  piston  drills. 

"No  special  skill  is  required  to  operate  a  hammer  drill  and 
herein  lies  one  of  its  greatest  advantages.  Only  a  skilled  machine 
man  can  overcome  a  'fitchered'  hole,  start  a  difficult  hole,  or 
determine  the  proper  feed  and  stroke,  thus  getting  maximum 
results  with  the  piston  drill.  But  a  half  day's  work  will 
familiarize  any  intelligent  laborer  with  a  hammer  drill.  One 
skilled  miner  can  direct  or  'point'  the  holes  for  half  a  dozen  or 
more  hammer  drills  —  a  most  important  item  where  good  men 
are  hard  to  get. 

"It  is  no  exaggeration  to  say  that  95  per  cent,  of  the  stoping 
work  in  the  mines  of.  the  world  is  still  being  done  by  hand.  It  is 
also  a  fact  that  one  hammer  drill  will  average  an  equivalent  of 
six  to  fifteen  hand  drillers.  Good  labor  is  every  year  more  scarce. 
If  10  hammer  drills  will  do  the  work  of  100  miners,  they  are  cer- 
tainly a  good  investment.  With  a  limited  force  provided  with 
these  drills,  ten  times  the  drilling  can  be  done,  and  the  prcduc- 


HAMMER  DRILLS  83 

tion  correspondingly  increased,  thus  getting  cheap  machine  re- 
sults in  one  year  which  would  otherwise  take  much  longer. 

"This  advantage  goes  still  farther.  Much  of  the  economy  of 
mining  depends  on  the  holes  being  properly  and  skilfully  placed 
to  bring  out  the  maximum  quantity  of  ore  with  the  minimum 
powder  charge,  and  with  the  minimum  amount  of  undesirable 
waste  rock.  It  is  certainly  true  that  the  average  skill  of  10 
selected  hammer-drill  men  will  be  higher  than  that  of  a  gang  of 
100  hand  drillers.  The  importance  of  this  point  in  its  bearing 
on  low  mining  costs  and  improved  operating  conditions  will  be 
appreciated  by  every  mine  manager. 

"The  hammer  drill  enables  the  miner  to  follow  a  vein  in  a 
stope  only  wide  enough  for  his  body,  bringing  out  the  ore  with 
maximum  values  and  with  the  minimum  of  waste  rock  to  be 
sorted  or  treated.  One  instance  may  be  noted.  A  2j-in.  piston 
drill  stoping  in  a  14  to  18  in.  vein  gave  ore  values  of  $30  to  $35 
per  ton.  The  substitution  of  a  hammer  drill  brought  out  one- 
third  more  ore  from  the  stope  18  in.  wide  than  the  piston  drill 
brought  out  from  a  3|-ft.  stope;  and  values  at  once  ran  up  from 
$80  to  $90  per  ton.  Hoisting,  sorting,  and  powder  costs  were 
cut  in  two;  timbering  costs  were  reduced  two-thirds;  and  the 
total  ore  tonnage  was  increased.  Power  cost  per  shift  for  one 
drill  was  reduced  from  $3  to  $1.  In  this  case  the  user  figured 
that  the  smaller  machine  was  worth  $1000  per  month  to  him. 

"The  experience  of  the  most  careful  users  has  shown  that 
the  hammer-drill  brings  about  a  most  important  reduction  in 
the  cost  of  explosives.  The  average  powder  man  will  load  a  hole 
to  the  limit,  regardless  of  whether  so  much  powder  is  needed  or 
not.  The  small  hole  made  by  the  hammer  drill  reduces  the 
likelihood  of  over-charged  holes  or  over-shooting  and  the  objec- 
tionable pulverizing  of  rich  ore. 

"But  as  the  diameter  and  depth  of  hole  best  suited  to  move 
a  given  amount  of  rock  diminishes,  a  point  is  reached  where  the 
economical  field  of  the  standard  drill  merges  into  one  best  covered 
by  the  hammer  drill.  The  dividing  line  is  reached  (this  does  not 
apply  to  machines  of  the  Leyner  type),  in  mining  work,  for  in- 
stance, where  narrow  stopes  are  encountered,  where  raises  have 
to  be  driven :  as  in  the  caving  system,  in  underhand  stoping,  where 
a  thin  vein  must  be  worked  with  a  breaking  of  waste  rock,  or 
wherever  small,  comparatively  shallow  holes  (usually  up-holes) 


84  ROCK  DRILLS 

require  easy  placing  of  the  machine  used  and  economical  drill- 
ing through  reduced  'dead  time'  become  determining  factors. 
This  means  that  as  large  a  proportion  of  the  time  as  possible 
shall  be  spent  in  actual  drilling  rather  than  in  setting  up  and 
moving.  From  the  line  here  denned  the  field  of  the  hammer 
drill  extends  down  to  the  drilling  of  the  smallest  holes  for  trim- 
ming pop  shots  and  similar  work." 


IV 
ELECTRIC   DRILLS 

THE  comparatively  high  power  consumption  and  low  efficiency 
per  unit  of  power  employed  by  standard  rock  drills  have  always 
encouraged  inventors  to  seek  some  machine  in  which  better  results 
could  be  obtained.  Electricity  appeared  to  be  just  the  force 
required.  It  could  be  transmitted  by  wires  instead  of  by  cum- 
bersome pipes.  Machines  for  performing  almost  every  other 
kind  of  work  had  been  successfully  run  by  means  of  electricity, 
with  a  high  mechanical  efficiency. 

The  designers  of  electric  drills  found,  however,  that  they  were 
entering  a  new  field  of  work  with  many  unforeseen  difficulties. 
Electricity  is  a  force  particularly  adapted  for  producing  rotation, 
and  could  rotary  drills  or  augurs  have  been  used  for  boring  hard 
rock,  the  design  of  a  simple  effective  machine  adapted  for  working 
underground  might  have  been  easy.  Such  rotary  drills  are  work- 
ing in  soft  rock  and  coal;  some  are  employed  in  the  Cleveland 
Ironstone  district  in  England.  The  diamond  drill  bores  hard 
rock  by  this  means,  but  is  too  heavy,  complicated,  and  expensive, 
and  does  not  work  rapidly  enough  to  compete  with  air  machines. 

The  principle  of  the  electric  solenoid  was  first  taken  advan- 
tage of  to  produce  percussive  action,  similar  to  that  of  a  piston 
machine.  Siemens-Halske  built  the  first  percussion  electric 
drill  about  1879.  In  the  Marvin  Sandy  croft  drill  the  soft  steel 
piston,  of  which  the  chuck  is  an  extension,  works  in  a  cylinder 
surrounded  by  two  coils  of  wire.  The  coils  are  made  to  alter- 
nately attract  the  piston  backwards  and  forwards.  The  piston 
and  tool  are  rotated  by  the  usual  rifle  bar,  ratchet  wheel,  and 
pawls.  There  is  a  cushion  spring  to  check  or  cushion  the  back 
stroke.  The  energy  thus  stored  is  given  out  to  assist  the  forward 
blow.  The  current  is  brought  by  a  three- wire  cable,  the  center 
wire  being  common  to  both  circuits.  A  special  make  of  two- 
phase  alternator,  with  separate  exciter,  sends  the  current  alter- 
nately every  half  revolution  to  back  and  front  coils.  The  dynamo 

85 


86  ROCK  DRILLS 

runs  about  400  revolutions  per  minute.  The  drill  strikes  a  cor- 
responding number  of  blows.  The  copper  wire  in  the  coils  is  of 
square  section,  insulated  by  mica.  They  are  solidly  wound  on  a 
steel  tube,  enclosed  in  the  casing,  and  thus  shifting,  a  wear  of 
insulation  is  guarded  against.  Losses  of  power  are  said  to  amount 
to  6|  h.p.  for  1J  h.p.  exerted  in  actually  cutting  rock.  The  chief 
electrical  loss  is  found  in  the  heating  of  the  solenoids.  The  drill 
heats  rapidly,  owing  to  the  reversals  of  current.  This  drill  is 
heavy  in  comparison  with  its  power;  but  has  found  a  limited 
field  for  useful  employment  in  quarries  and  other  open-air  work. 
It  cannot,  I  think,  compete  with  the  standard  rock  drill  in  speed 
of  drilling,  handiness,  and  reliability  in  underground  work.  The 
Edison  drill  is  of  same  class;  also  the  Van  Depoele;  voltage,  110- 
220;  weight,  400-450  lb.;  stroke,  300-600. 

The  second  class  of  electric  drills  includes  the  Durkee,  Dietz, 
and  the  Siemens-Halske.  These  place  the  motor  in  a  separate 
case,  and  it  is  connected  with  the  drill  by  a  flexible  shaft. 

The  third  class  has  the  motor  mounted  on  or  near  the  drill 
itself  or  rigidly  connected  with  it.  This  includes  the  Adams  and 
the  Gardner,  which  is  a  hammer  drill. 

The  Siemens-Halske,  Gardner,  Adams,  Durkee,  and  Dietz 
drills  use  a  crank-shaft.  In  all  these  drills  rotary  motion  has  to 
be  converted  into  reciprocatory  motion,  involving  the  use  of 
springs,  cams,  journals,  and  bearings.  If  the  motor  is  on  the 
machine,  the  jar  caused  by  its  working  and  by  the  drill  sticking 
sometimes  tends  to  destroy  the  insulation;  short-circuiting  may 
occur  and  the  armature  become  burnt  out.  The  plan  of  effecting 
this  transmission,  as  in  the  Siemens-Halske  machine,  is  to  have 
the  flexible  shaft  drive  the  crank-shaft  by  closed  gearing.  The 
crank-shaft  carries  a  heavy  fly-wheel  on  one  end,  and  the  other  a 
pin,  cam,  or  draw  bar,  or  a  crank  disc,  having  a  throw  of  about 
3  inches.  This  pin  engages  and  moves  a  sliding  cylinder  holding 
two  powerful  springs.  As  the  travel  of  the  draw  bar  is  limited, 
and  the  cam  must  have  certain  definite  limits  of  motion,  the 
connection  between  it  and  the  piston  must  be  made  flexible  to 
allow  the  draw  bar  to  continue  its  motion  when  the  drill  steel 
gets  stack;  otherwise  the  motor  would  be  stalled,  or  some  con- 
nection broken.  These  springs  must  be  strong  enough  to  strike 
a  powerful  blow  of  100-foot  lb.  or  more.  The  momentum  of  the 
moving  piston  throws  it  out'  at  the  end  of  each  stroke,  and  the 


ELECTRIC  DRILLS 


87 


piston  actually  travels  twice  the  length  of  the  crank.  The  fly- 
wheel is  fitted  to  absorb  any  irregular  stresses  and  to  prevent 
shock  to  the  gearing,  crank-pin,  shaft,  and  bearings  when  the 
drill  has  to  pull  back;  also  when  the  crank  passes  back  of  center 
position;  at  the  beginning  of  forward  stroke,  and  when  the  drill 
strikes.  It  is  thus  obvious  that  the  electric  drill  cannot  be  of  as 
simple  construction  as  the  standard  rock  drill  of  piston  or  ham- 
mer type  worked  by  air. 

Siemens-Schuckert    Drill.  —  A    crank   impact  drill    has   been 


ii 


FIG.  72  —  Deitz  drill. 

designed  recently  by  the  Siemens-Schuckert  works.  It  is  operated 
by  a  1  h.p.  motor,  fitted  directly  to  the  drill,  and  is  said  to  be  far 
more  efficient  than  the  usual  design  of  rock  drill  with  flexible 
shaft  and  motor  box.  The  electro-motor  is  placed  in  a  saddle  in 
the  back  of  the  drill  and  is  readily  removable.  Like  the  drill 
itself,  it  is  enclosed  in  a  dust  and  water-proof  casing.  According 
as  the  drill  is  working  on  the  right  or  left  side  of  the  supporting 
column,  the  motor  is  placed  above  or  below  the  drill.  This  differ- 
ence in  the  position  of  the  motor,  however,  exerts  no  influence 


ROCK   DRILLS 


on  the  working  of  the  drill ;  it  may 
be  used  as  well  on  a  horizontal 
column  or  transportable  supports 
provided  it  is  fitted  with  a  special 
feeding  slide. 

Gardner  Electric  Drill.  —  In  the 
Gardner  drill,  the  power  is  trans- 
mitted, similar  to  the  Siemens  drill, 
to  a  crank-shaft,  the  crank  of  which 
works  in  a  special  shaped  slot  in 
a  crosshead  so  that  a  quarter  revo- 
lution strikes  a  blow.  The  next 
withdraws  the  drill,  rotating  it 
partially,  and  during  the  last 
quarter  the  drill  remains  station- 
ary. On  the  opposite  end  of  the 
crank-shaft  is  a  fly-wheel  which 
absorbs  energy  during  the  last 
quarter  of  the  stroke,  and  gives  it 
out  during  the  first,  thus  overcom- 
ing any  tendency,  of  the  quick  for- 
ward and  slow  return  reciprocation 
of  the  crosshead,  to  impart  irregu- 
larity to  the  rotation  of  the  gear- 
ing. Buffer  springs  connect  the 
crosshead  to  piston  and  drill.  The 
largest  Gardner  drill  uses  2  h.p. 
and  strikes  550  blows  per  minute. 
The  drill  and  motor  together  weigh, 
it  is  claimed,  less  than  that  of  an 
air  drill  of  similar  power. 

Deitz  Drill. —  Referring  to  Figs. 
72  and  73,  the  drill  operates  as 
follows:  As  the  yoke  A  moves  for- 
ward, the  piston  B  compresses  the 
air  in  the  chamber  C;  this  forces 
the  cylindrical  air  hammer  D 
against  the  tappet  E,  which  strikes 
the  head  of  the  drill  steel  at  F. 
The  reverse  stroke  of  yoke  A  then  moves  back  the  piston 


ELECTRIC   DRILLS  89 

B,  which  compresses  the  air  in  chamber  G,  which  brings  back  the 
cylindrical  air  hammer  D,  the  momentum  of  which  compresses 
again  the  air  in  chamber  C,  at  the  time  that  the  piston  B  reverses 
for  the  return  stroke  forward. 

Thus  the  speed  of  the  hammer  D,  forward,  is  almost  twice 
the  speed  as  the  piston  B,  for  the  reason  that  the  hammer  D  does 
not  start  forward  until  the  piston  B  has  about  finished  half  of  its 
stroke  forward.  This  delivers  a  tremendous  blow  upon  the  drill 
steel,  and  at  the  same  time  transmits  no  perceptible  jar  to  the 
mechanism  of  the  drill,  for  the  reason  that  the  piston  is  cushioned 
on  air,  both  at  the  forward  and  backward  strike;  the  cylindrical 
hammer  merely  floating  on  the  air  cushions. 

In  the  large  size  Model  D  drill,  the  hammer  weighs  12 
lb.,  and  strikes  600  blows  per  minute.  In  the  smaller  size 
Model  E  drill,  the  hammer  weighs  six  lb.,  and  strikes  1,000 
blows  per  minute. 

Locke  Drill.  —  In  the  Locke  drill,  an  attempt  is  made  to  mount 
the  motor  on  the  drill.  The  crank  axle  is  driven  direct  by  means 
of  gearing,  and  is  connected  to  the  piston  by  a  helical  spring. 
The  speed  of  the  motor  is  so  adjusted  that  the  drill  strikes  the 
blow  on  the  backward  stroke  of  the  crank.  This  could  be  done 
while  the  spring  retained  the  exact  elasticity  required  and  the 
drill  the  proper  speed. 

Locke  contends  that  the  insulation  difficulty  can  be  overcome 
by  having  the  axis  of  the  motor  parallel  to  that  of  the  drill,  so 
the  vibration  will  not  throw  the  brushes  off  the  commutator,  thus 
causing  sparking.  The  motor  is  firmly  attached  to  the  cradle  of 
drill,  and  a  telescopic  shaft  is  used  to  transmit  the  power  as  the 
drill  is  fed  forward.  He  states  that  his  drill  has  been  in  use  15 
months  in  Colorado  without  any  injury  to  the  insulation.  He 
contends  that  springs  will  stand  if  not  over-compressed  to  more 
than  J  of  their  length.  Springs  have  been  in  use  for  six  months 
on  a  drill,  striking  420  blows  per  minute.  He  thinks  that  the 
advantages  due  to  initial  low  cost  for  installing  electric  gener- 
ators, and  the  less  cost  of  wires  compared  with  air  pipes  and 
their  maintenance,  together  with  power  costs  at  only  10  per 
cent,  that  of  air  drills,  make  the  development  of  the  electric 
drill  certain. 

The  following  is  the  result  of  a  test  carried  out  in  Germany 
between  the  Siemens-Halske  electric  drill  and  a  standard  air  drill. 


90 


ROCK  DRILLS 


Work  done  in  Bore  Hole 

Air  Drill 

Electric  Drill 

Cubic  inches  per  min                             

2.75 

3.00 

Ft  Ibs  per  min 

11.664 

12.960 

Consumption  of  power  in  generator  and  motor,  ) 

10  H.  P. 

1.7  H.  P. 

the  power  being  transmitted  2000  yds.  .  .  .  ) 

324,000  ft.  1 

bs.,  min.  54,000 

Total  efficiency,  per  cent  

3.6 

24 

Electric  Drill  Results.  —  Gliickauf,  of  June  4,  1904,  publishes 
some  very  interesting  details  regarding  the  working  of  an  electric 
rock-drill  installation  at  the  iron  ore  mines  at  Peine,  Hanover, 
Germany. 

"The  installation  referred  to  comprises  10  electric  percus- 
sion Siemens-Halske  rock  drills,  driven  by  2 15- volt  three-phase 
motors.  The  primary  plant  consists  of  a  10  kw.  three-phase 
generator  driven  by  a  gas  engine  using  blast-furnace  gas.  The 
current  is  generated  at  1,000  volts,  and  is  transformed  to  217 
volts  in  the  mine. 

"It  has  been  found  essential  for  the  efficient  working  of  these 
electric  drills  to  give  them  frequent  and  careful  inspection,  in 
order  to  make  certain  of  even  the  smallest  part  being  in  good 
working  condition. 

"Apart  from  this  the  drills  seem  to  have  given  good  results, 
and  the  repairs  necessary  have  by  no  means  been  heavy.  The 
most  troublesome  part  appears  to  have  been  the  crank-pin,  but 
it  is  now  the  practice  to  replace  it  after  50  hours'  work.  Another 
weak  spot  is  the  spring  used,  and  it  was  found  that  the  average 
life  of  a  spring  is  from  30  to  33  shifts. 

"The  consumption  of  energy  per  drill  amounts  to  5.5  amp. 
at  220  volts,  or  about  1.7  b.h.p.,  so  that  the  10  kw.  generator, 
stationed  over  a  mile  from  the  mine,  is  large  enough  for  six  drills. 

"The  cost  of  one  drill  complete  with  wall  box,  flexible  shaft, 
motor,  cable,  column,  and  125  bits  amounted  to  about  £233, 
and  as  two  drills  were  used  in  one  shaft,  the  total  cost  was  £466, 
plus  £16  for  a  tool  case,  or  £482. 

"The  working  expenses  for  the  year  June  1,  1901,  to  May  31, 
1902,  were  as  follows,  there  being  two  drills  constantly  in  use: 

"Cost  of  energy,  £11  10s.;  spare  parts,  £64  10s.;  wages  of 
fitters,  £40  10s.;  materials,  £23  10s.;  blacksmiths'  wages,  £36 


ELECTRIC   DRILLS 


91 


10s.;  new  drills  and  drill  sharpening,  £39  10s.;  interest  on  capital 
and  depreciation  on  six  drills,  including  portion  of  switchboard, 
water  supply,  etc.,  £125  Os.;  total,  £341  10s. 

"The  work  done  during  the  year  amounted  to  1,652  drill 
shifts,  or  a  cost  per  drill  per  shift  of  4.134  shillings.  From  June  1 
to  November  30,  1902,  seven  drills  were  in  use,  and  the  cost  per 
drill  per  shift  amounted  to  3.68  shillings,  including  all  the  items 
previously  mentioned,  along  with  lubricating  oil,  waste,  etc. 

The  following  are  some  particulars  of  the  performances  of 


FIG.  74.  —  Adams  electrically  driven  rock  drill. 

electric  drills  in  actual  work.  Gillette  gives  the  following  data 
regarding  the  work  of  four  Gardner  electric  drills  in  an  hydraulic 
mine,  Bullion,  B.  C.  Three  2-h.p.  drills,  and  one  l|-h.p.  drill 
were  in  use  two  years;  each  of  the  larger  machines  has  drilled  13 
holes  8  ft.  deep  in  augite-diorite  and  porphyrite  in  a  10-hour 
shift;  the  cost  per  shift,  for  3  drills,  $31.55,  for  312  ft.  drilled. 
Thirty-six  Box  electric  drills  were  installed  in  the  D.  L.  &  W.  R.  R. 
Tunnel  at  Hoboken,  New  Jersey,  August,  1906,  but  replaced  by 
standard  piston  air  drills,  January,  1907. 

Adams  Electric  Drill.  —  Figs.  74  and  75  will  show  the  various 


92 


ROCK   DRILLS 


parts  of  the  drill  assembled.  The  motor  is  suspended  in  a  fork 
which  is  booted  to  the  guide  shell,  and  can  be  placed  in  four 
different  positions,  viz.:  on  either  side,  front  or  back,  as  con- 
ditions may  require.  Connection  is  made  from  the  motor  to  the 
controller  by  means  of  a  flexible  armored  cable  with  contact  box 
having  spring  contacts  and  a  rubber  protector,  which  on  being 
placed  in  position  makes  a  perfectly  waterproof  connection.  The 


FIG.  75.  —  Adams  drill  on  column  with  internal  mechanism  removed. 

power  is  transmitted  to  the  drill  by  means  of  a  loose  square  steel 
rod  running  through  the  armature  shaft  in  the  motor,  and  a  set 
of  bevel  gears  on  the  drill,  which  impart  motion  to  the  crank- 
shaft, thence  to  the  draw  bar,  which,  in  turn,  reciprocates  the 
piston.  The  piston  is  cushioned  by  two  gangs  of  helical  springs, 
which  add  to  the  force  of  the  blow  and  render  sticking  of  the 
steel  in  a  hole  a  rare  occurrence.  Each  spring  is  provided  with 
a  rubber  auxiliary  cushion,  which  prevents  excessive  breakage. 
This  arrangement  also  permits  the  drill  to  be  operated  at  full 


ELECTRIC   DRILLS 


93 


speed  without  hitting  the  rock,   and  with  no  damage  to  the 
machine,  and  in  addition  makes  a  perfect  reamer. 

The  rotation  of  the  piston  is  secured  by  a  double  set  of  ratchets, 
one  working  in  a  straight  and  the  other  in  a  spiral  groove  in  the 
piston.  The  spiral  groove  is  milled  so  as  to  cause  the  piston  to 
turn  on  the  backward  stroke,  the  straight  ratchet  preventing  it 
from  turning  on  the  forward  stroke.  The  rotation  after  each 
blow  is  about  ^V  of  a  complete 
revolution,  and  when  operated 
at  full  speed  will  make  thirty 
turns  per  minute.  The  piston 
and  ratchets  are  case-hardened 
to  provide  against  wear.  Each 
wheel  has  six  pawls  with  phos- 
phor bronze  springs.  The  pis- 
ton is  guided  by  a  head  which* 
works  in  the  draw  bar  and  body, 
and  a  long  bushing  in  front  of 
the  ratchets,  this  head  being- 
held  to  the  piston  by  means  of  a 
removable  key.  The  crank-pin 
has  a  hardened  box,  divided  in 
halves,  operating  in  the  draw 
bar. 

In  order  to  protect  the  ma- 
chine and  springs  when  feeding 
too  close  to  the  rock,  or  in  deep 
holes,  a  rubber  nose  buffing  col- 
lar is  placed  in  front  of  the  nose 
bushing,  directly  behind  the  FlG-  76.  -  Adam^s  ^ectrically  driven 
chuck.  Side  doors  are  provided 

in  the  body  for  removing  and  inspecting  the  springs  without 
taking  the  machine  apart.  The  entire  internal  mechanism  can 
be  removed  by  taking  off  one  nut  at  the  back  of  the  draw  bar, 
and  removing  the  spanner  sleeve  in  front.  The  internal  mechan- 
ism can  then  be  drawn  out  in  front.  To  remove  the  parts  from 
the  piston,  all  that  is  required  is  to  drive  out  a  key  in  the  pis- 
ton head.  The  draw  bar,  spring  spacer,  and  ratchets  may  then  be 
lifted  off  the  piston.  The  steel  is  held  by  the  usual  form  of 
U-bolt  chuck  common  to  air  drills,  and  is  simple,  durable,  and 


94  ROCK  DRILLS 

effective.  All  bearings,  as  well  as  other  moving  parts,  are  case- 
hardened,  ground,  and  lapped,  giving  a  hard  surface  and  a 
soft,  strong  interior.  Provision  is  made  at  all  points  possible  for 
taking  up  wear  or  lost  motion,  either  by  taking  out  a  shim  or 
adjusting  the  taper  bearings.  The  reader's  attention  is  called  to 
cuts,  illustrating  how  this  may  be  accomplished.  This  enables 
the  operator  to  have  a  smoothly  running  machine  at  all  times, 
as  well  as  insuring  a  low  cost  of  maintenance. 

The  drill  strikes  600  blows  per  minute  when  running  at  full 
speed,  the  motor  running  at  1800  r.p.m.,  the  gears  making  a 
three  to  one  reduction.  The  weight  of  the  drill  complete,  Fig.  76, 
is  approximately  295  lb.,  the  D.  C.  motor  150  lb.,  the  A.  C. 
motor  125  lb. 

Edward  Stoiber,  of  Colorado,  states  that  he  tried  the  Siemens 
drills,  but  they  failed  to  stand  the  rough  usage  of  mining  condi- 
tions in  hard  ground.  The  following  is  given  in  the  Engineering 
and  Mining  Journal,  as  comparative  results  of  2f-in.  air  piston 
drills  and  2-in.  Adams  electric  drills,  air  pressure  80  lb. 


Air  Drill 

Adams'  Electric 
Drill 

Actual  time  drilling,  hrs.  . 

317 

100 

Ft.  drilled   

1279 

253 

Ft.  drilled  per  hour    . 

4 

2.53 

Time  lost  for  repairs  . 

0 

17 

Boring  was  in  black  diabase,  10-hour  shifts  being  worked. 
The  electric  drills  did  good  work  in  driving  the  Raibl  adit  in 
Corinthia,  Europe. 

Rotary  Electric  Drills.  —  Mr.  H.  W.  Appleby  states  that  in 
the  Cleveland  iron  ore  mine,  Cleveland,  Yorkshire,  England,  one 
air  compressor  was  working  six  3i-in.  diameter  air  drills.  Indi- 
cator diagrams  showed  an  average  of  111.06  h.p.  developed,  or 
18.5  h.p.  per  drill.  This  engine  was  replaced  by  an  electric 
generator,  a  smaller  engine  and  six  electric  rotary  rock  drills. 
When  these  drills  were  working  (and  it  is  stated  breaking  as 
much  rock  as  before),  the  new  engine  showed  only  24.52  i.h.p., 
being  a  reduction  of  77.91  per  cent,  in  power  used.  Costs  in 
pence  per  ton  are  as  follows: 


ELECTRIC   DRILLS 


95 


Air  Drill 

Electric  Drill 

Oil,  stores  and  labor    •  
Coal                                                  

0.297 
0.242 

0.253 
0.108 

Repairs,  making,  sharpening  drills,  and  maintain- 
ing pipes  or  cable 

0.340 

0  170 

Total        ... 

0.879 

0.531 

In  the  Engineering  and  Mining  Journal,  W.  H.  Yeandle,  Jr., 
gives  the  results  obtained  from  working  three  Box  drills  for  ten 
months  at  El  Banco  mine,  Oaxaca,  Mexico.  Two  drills  were  new. 
one  being  kept  as  an  extra.  Drills  were  run  12-hour  shifts,  except 
Sundays,  and  were  operated,  repaired,  and  cleaned  by  Mexican 
labor.  The  drills  worked  in  metamorphosed,  calcareous  slate, 
pyroxene,  andesite,  and  quartz  vein  matter,  all  being  hard  rock. 
The  drills  worked  under  hard  conditions,  as  the  mine  was  wet, 
hot,  and  foggy.  Each  drill  put  in  one  round  of  16  five-foot  holes 
in  24  to  28  hours.  The  extra  parts  used  during  12  months  included 
one  rheostat  or  controller;  2  sets  brush  holders;  4  sets  graphite 
motor  bearings;  36  brushes;  6  sets  chuck  gears  and  shaft;  1  crank- 
shaft and  bevel  gears;  3  full  sets  of  bearings;  2  chuck  blocks  and 
gears;  1  air  cylinder  shell,  hammer,  wire,  and  insulation.  Those 
parts  transmitting  turning  motion  to  the  chuck  blocks  and  steel 
were  worst,  as  the  water  injection  system  failed  and  the  bits 
jammed  in  holes.  Fitchering  was  uncommon.  Vibration  caused 
the  use  of  the  large  number  of  brushes,  etc.,  and  each  commutator 
had  to  be  turned  down.  The  drills  could  not  be  run  at  full  speed 
or  current  owing  to  motor  heating,  and  excessive  vibration;  drill 
runners  operated  with  one-half  or  three-fourths  power,  thus  burn- 
ing out  the  rheostats.  Short-circuiting  was  common.  The  drills, 
though  far  less  efficient  than  air  drills,  did  better  and  cheaper 
work  than  the  hand  labor  available.  The  makers  now  claim  to 
have  greatly  improved  the  water  injection  system,  rendering  the 
drill  more  efficient. 

ELECTRIC  AIR  DRILL 


The  Temple-Ingersoll  electric  air  drill,  Fig.  77,  is  a  compara- 
tively new  machine,  and  I  take  the  following  description  from 


ROCK   DRILLS 


the  Bi-monthly  Bulletin  (November,  1907)  of  the  American  Insti- 
tute of  Mining  Engineers: 

Many  features  of  electrical  transmission  are  undoubtedly  con- 
venient and  economical;  but  the  direct  application  of  the  electric 
current  in  rock  drilling  has  long  been  a  baffling  problem;  of  which, 
in  my  judgment,  the  machine  here 
described    has   furnished   the   first, 
and  thus  far  the  only  satisfactory 
solution,    by    combining     the     ac- 
knowledged advantages  of  air-driven 
percussion  with  the   acknowledged 
advantages  of  electric  power  trans- 
mission,   while    avoiding    the     ac- 
knowledged disadvantages  of  both 
systems. 

This  drill  is  correctly  desig- 
nated; it  is  not  an  electric  drill, 
but  more  completely  an  air  drill 
than  any  other  in  existence,  because 
it  can  be  driven  only  by  air  and  not, 
like  other  air  drills,  by  steam  also. 
Yet,  while  it  is  thus  distinctly  air- 
operated,  the  power  transmission  is 
electric,  and  the  sole  connection  of 
the  drill  with  the  power-house  is 
made  by  the  electric  wire,  air  com- 
pressors and  pipe  lines  being  entirely 
superseded. 

Very  near  the  drill,  and  con- 
nected to  it  by  two  short  lengths 
of  hose,  is  a  small  air  compressor, 
or,  more  properly,  a  pulsator, 
mounted  upon  a  little  truck.  This 

constitutes  the  entire  apparatus  of  a  single  drill.  Each  drill  is 
accompanied  by  its  individual  pulsator,  and  each  pulsator  is  con- 
nected to  the  line  of  wire  from  the  power-house. 

The  usual  drill  shell  is  employed,  and  may  be  mounted  upon 
tripod,  bar,  or  column,  according  to  the  work.  The  drill  cylinder, 
fitted  to  slide  in  the  shell,  is  moved  forward  or  backward  by  the 
feed-screw.  The  cylinder  is  as  simple  as  can  be  imagined:  a 


ELECTRIC   DRILLS  97 

straight  bore,  having  at  each  end  a  large  opening.  The  piston 
also  is  plain,  much  shortened  in  the  body,  with  a  large  piston- 
rod,  which  has  a  long  bearing  in  a  sleeve-elongation  of  the  cylinder. 

Upon  a  truck  is  mounted  an  electric  motor,  geared  to  a  hori- 
zontal shaft,  with  cranks  on  each  end,  which  drive  two  single- 
acting  trunk  pistons  making  alternate  strokes  in  vertical  air 
cylinders.  One  of  these  air  cylinders  is  connected  by  the  hose 
to  one  end  of  the  drill  cylinder  and  the  other  end  of  the  drill 
cylinder  is  connected  by  the  other  hose  to  the  other  air  cylinder. 
The  air,  therefore,  in  either  cylinder,  in  its  hose  and  in  the  end 
of  the  drill  cylinder  to  which  it  is  connected,  remains  there  con- 
stantly, playing  back  and  forth  through  the  hose  according  to 
the  movements  of  the  parts,  being  never  discharged,  and  only 
replenished  from  time  to  time  to  make  up  for  leakage.  The 
propriety  of  calling  the  apparatus  a  pulsator  instead  of  a  com- 
pressor is  evident. 

Details  of  Operation.  —  The  essential  details  of  the  cycle  of 
operation  will  be  easily  understood.  We  may  assume,  to  begin 
with,  that  the  entire  system  is  filled  with  air  at  a  pressure  of  30 
or  35  Ib.  This  pressure  being  alike  upon  both  sides  of  the  drill 
piston,  it  will  have  no  tendency  to  move  in  either  direction.  If, 
now,  the  motor,  instead  of  being  at  rest,  is  assumed  to  be  in 
motion,  one  pulsator  piston  will  be  rising  in  its  cylinder  and  the 
other  piston  will  be  descending  in  its  cylinder;  and,  as  a  conse- 
quence, the  pressure  upon  one  side  of  the  drill  piston  will  be 
increased  and  the  pressure  upon  the  other  side  will  be  proportion- 
ately reduced,  this  difference  of  pressure  causing  the  drill  piston 
to  move  and  make  its  stroke.  Just  before  the  end  of  this  stroke, 
the  movement  of  the  pulsator  pistons  is  reversed,  and  the  pre- 
ponderance of  pressure  is  transferred  to  the  other  side  of  the 
piston,  causing  a  stroke  in  the  other  direction  —  and  so  on  con- 
tinuously. The  drill  thus  makes  a  double  stroke,  or  at  least 
receives  a  double  impulse,  for  each  revolution  of  the  pulsator 
crank-shaft. 

The  drill  cylinder,  while  generally  similar  to  that  of  the  air 
-or  steam  drill,  is  in  many  respects  quite  different;  and  especially 
is  it  remarkable  for  its  simplicity.  The  usual  operating  valve- 
chest;  the  valve  and  the  complicated  means  for  operating  it;  the 
main  air  ports  and  the  intricate  little  passages  in  and  connected 
with  the  chest  —  are  all  absent,  and  nothing  takes  their  place. 


98  ROCK  DRILLS 

The  cylinder  heads  are  both  solid  and  both  fastened  securely  in 
place.  The  split  front  head,  the  yielding  fastenings  for  both 
heads,  the  buffers,  the  springs,  the  side-rods,  etc.,  of  other  drills, 
have  all  been  banished.  The  cylinder  is  absolutely  plain,  with 
direct  openings  into  the  interior,  and  a  boss  at  each  end  to  which 
the  hose  is  attached. 

The  piston  also  has  been  simplified.  The  device  for  securing 
rotation  is  necessarily  retained;  but  the  enlargement  at  the  end 
of  the  piston-rod,  which  constituted  the  chuck  and  necessitated 
the  split  front  head,  has  been  discarded.  The  piston-rod  is  much 
enlarged  throughout,  and  a  simple  but  effective  self-tightening 
chuck  is  slipped  upon  the  end  of  it. 

The  compressor  or  pulsator  cylinders  are  likewise  simple. 
There  are  no  valves  for  either  inlet  or  discharge,  and  there  is 
neither  jacketing  nor  the  slightest  need  of  it.  The  heating  of 
the  air  by  the  compression  stroke  is  compensated  by  the  cooling 
which  attends  the  re-expansion  of  the  same  air,  so  that  it  does 
not  become  increasingly  hot  and  heat  the  parts  of  the  machine 
with  which  it  comes  in  contact. 

Air  Pressure.  —  In  the  foregoing  description  of  the  principle 
of  operation  I  assumed  a  mean  air  pressure  of  about  30  Ib.  in  the 
apparatus.  It  may  be  asked  how  this  pressure  is  secured  and 
maintained.  When  the  pulsator  is  in  operation,  the  air  pressure 
in  the  cylinders  alternately  rises  above  and  falls  considerably 
below  the  mean.  At  a  certain  point,  indeed,  it  is  below  that  of 
the  atmosphere;  and  at  this  point  a  little  valve  is  provided,  which 
admits  more  or  less  air,  until  a  sufficiency  has  been  provided. 
At  the  beginning  of  operation  the  influx  of  air  is  rapid,  so  that 
no  time  is  lost  in  getting  sufficient  pressure  to  begin  with.  The 
admission  of  air  and  also  the  apportionment  of  relative  volumes 
thereof  to  the  two  ends  of  the  drill  cylinder  are  easily  adjusted 
by  the  operator. 

The  electric-air  drill  is  not  troubled  by  the  freezing  up  or 
choking  of  the  exhaust,  because  there  is  no  exhaust.  Moreover, 
the  air  does  not  accumulate  moisture,  and  the  temperature  does 
not  fall  to  the  freezing-point.  Again,  air  becomes  and  remains 
a  constant  vehicle  for  the  conveyance  and  distribution  of  the 
lubricant.  A  certain  amount  of  oil  being  contributed  to  the 
system  at  regular  intervals,  it  would  be  more  difficult  to  prevent 
than  to  insure  its  reaching  every  working  part. 


ELECTRIC   DRILLS  99 

The  length  of  hose  employed  seems  to  be  limited  to  about 
8  ft.  on  each  side.  The  hose  may  be  attached  to  either  side  of 
the  drill,  but  each  always  to  its  own  end  of  the  cylinder.  This 
length  of  hose  gives  all  necessary  liberty  for  the  location  of  the 
pulsator  truck  near  the  drill.  The  truck  (of  steel,  with  flanged 
wheels)  is  usually  made  for  the  standard  18-in.  mine  track,  but 
may  be  made  for  any  other  gage.  Special  care  in  leveling  is 
not  necessary,  since  the  pulsator  will  work  at  any  angle  at  which 
the  truck  can  stand. 

Electric  Current.  —  Either  a  direct  or  an  alternating  current 
motor  may  be  employed,  the  latter  being  preferred  because  it  is 
a  smaller,  lighter,  mechanically  simpler,  hardier  machine,  and 
more  nearly  "  fool-proof."  Four  different  speeds  may  be  obtained 
with  the  direct-current,  and  two  with  the  alternating-current 
motor  —  in  the  latter  case,  full  speed  for  steady  running  and  a 
considerably  lower  speed  for  starting  a  hole  or  working  through 
bad  ground,  with  immediate  transition  from  the  one  speed  to  the 
other,  as  required.  The  controller  is  on  the  top  of  the  motor 
and  the  operator  at  the  drill  can  start,  speed,  or  stop  the  motor 
by  simply  pulling  a  cord,  this  being  the  only  connection.  The 
electrical  connection  ends  at  the  motor;  both  the  hose  and  the 
cord  insulate  the  drill;  and  the  operator  is  never  exposed  to 
the  current. 

Sizes.  —  The  5-C  electric  air  drill  may  be  regarded  as  the 
full  equivalent  of  the  3.25-in  standard  air  drill  of  any  make;  of 
its  comparative  efficiency  something  will  be  said  later.  The 
power  requirement  for  this  drill  is  from  18  to  20  amperes  at  220 
volts,  or  from  9  to  10  amperes  at  440  volts  —  the  electrical  equiva- 
lent of  about  5  h.p.  The  system  being  a  closed  circuit,  this  is 
independent  of  conditions  of  altitude,  which  make  so  much 
difference  with  the  work  of  the  air  compressor  which  supplies 
the  ordinary  air  drill. 

The  4-C  electric-air  drill  uses  a  3-h.p.  motor,  and  is  a  much 
lighter  drill  throughout,  equivalent  to  a  2.75-in.  standard  air  drill. 
The  accompanying  table  on  page  100  gives  particulars  of  size, 
weight,  etc.,  of  both  of  these  drills. 

The  electric-air  drill  strikes  a  blow,  normally  so  much  harder 
than  that  of  the  air  drill  of  the  same  capacity  that  it  has  been 
found  advisable  in  many  cases  in  " dressing"  the  steel  bits  to 
make  them  blunter  or  thicker,  in  order  to  avoid  breakage.  The 


100  ROCK  DRILLS 

DIMENSIONS,  ETC.,  OF  TEMPLE-!NGERSOLL  ELECTRIC-AIR  DRILLS 


• 

5-C 

4-C~ 

Diameter  of  drill  cylinder  

5f  in. 

4.75  in. 

Length  of  stroke  
Length  of  drill  —  end  of  crank  to  end  of  piston  
Depth  of  hole  drilled  without  change  of  bit 

8    in. 
45    in. 
24    in. 

7       in. 
42       in. 
20       in. 

Depth  of  vertical  holes  machine  will  drill  easily  . 

16    ft. 

8       ft. 

Diameter  of  holes  drilled  from  1.75  to  2.75  in  
Strokes  per  minute  
Horse-power  (at  motor)  . 

425 
5 

1  to  1.5  in. 
460 
3 

practical  force  of  the  drill  had  not  been  computed  beforehand, 
but  was  demonstrated  in  extensive  practice  and  experiment,  and 
the  clear  and  sufficient  explanation  came  later. 

Piston.  —  The  drill  piston,  when  running  at  full  speed,  and 
making  a  stroke  for  each  rotation  of  the  pulsator  crank-shaft, 
does  not  strike  either  head.  The  hole  by  which  the  air  enters 
the  cylinder  from  the  hose  is  located,  not  at  the  extreme  end,  nor 
close  to  the  head  of  the  cylinder,  but  a  certain  distance  away,  so 
that  when  the  piston  approaches  the  head  a  portion  of  enclosed 
air  acts  as  a  cushion,  which  first  checks  the  piston  and  then  shoots 
it  back.  The  piston  thus  starts  upon  its  working  stroke  impelled 
by  a  certain  amount  of  force  which,  we  may  say,  has  been  saved 
over  from  the  preceding  stroke  to  be  utilized  for  this.  The  piston 
after  being  thus  started  is  driven  forward  by  an  air  pressure  which 
increases  as  it  advances,  the  pulsator  piston  being  in  the  attitude 
of  chasing  and  gaining  upon  the  drill  piston  for  a  considerable 
portion  of  the  stroke,  while  in  the  case  of  the  ordinary  drill  piston, 
driven  by  a  constant  flow  of  air  from  which  it  runs  away,  the 
pressure  must  constantly  diminish  as  the  piston-speed  is  acceler- 
ated. In  the  same  way,  by  the  action  of  the  other  pulsator  piston 
the  opposing  pressure  upon  the  advancing,  side  of  the  drill  piston  is 
a  diminishing  pressure  instead  of  the  constant  atmospheric  resist- 
ance, and  these  combined  cause  a  greater  unbalanced  difference 
of  pressures  upon  the  opposite  sides  of  the  drill,  a  more  rapid  accel- 
eration of  the  piston  movement,  and  a  consequent  higher  velocity 
and  force  at  the  moment  of  impact  of  the  steel  upon  the  rock. 

1  Size  3-C  is  equal,  in  capacity,  to  a  2-iri.  standard  air  drill;  4-C  is  equal  to 
a  2|-in.,  and  5-C  is  equal  to  a  3|-in. 


ELECTRIC   DRILLS  101 

Advantages.  —  Perhaps  the  most  gratifying,  and  also  surpris- 
ing, revelation  of  all  in  connection  with  the  electric-air  drill  is 
the  now  indisputable  fact  that  it  takes  only  from  one-third  to 
one-fourth  of  the  power,  at  the  power-house,  to  drive  it  to  do  the 
same  work.  This  is  accounted  for  by  the  fact  that  the  same  air 
is  used  over  and  over,  and  that  all  of  its  elastic  force  is  utilized 
in  both  directions  instead  of  exhausting  the  charge  for  each 
stroke  at  full  pressure.  There  are  also  no  large  clearance  spaces 
to  fill  anew  at  each  stroke,  as  these  spaces  are  never  emptied. 

A  valuable  feature  of  the  electric- air  drill  is  the  ability  to 
yank  the  bit  free  if  stuck  in  a  hole  and  immediately  continue  its 
work.  When  the  bit  of  the  electric-air  drill  sticks,  the  motor 
and  the  pulsator  pistons  do  not  stop.  If  the  drill  piston  is  mak- 
ing, say  400  strokes  a  minute,  as  soon  as  the  bit  becomes  stuck 
the  piston  will  receive  per  minute  400  alternate  thrusts  and  pulls 
with  full  force,  and  nothing  could  be  more  effective  for  freeing 
the  bit  than  these  alternate  thrusts  and  pulls. 

When  the  electric-air  drill  is  operated  without  its  own  gener- 
ating plant,  the  current  being  taken  from  a  large  power  company, 
some  very  low  figures  are  already  on  record.  At  Idaho  Springs, 
Colo.,  a  mine  shaft  was  put  down  67  ft.  in  24  shifts  and  the  total 
power  cost  was  $24  for  the  entire  work. 

Results  Obtained.  —  This  drill  has  been  before  the  public  five 
years,  and  several  hundred  are  in  use.  Some  of  the  work  done 
to  date  includes  2200  ft.  of  8  X  9  ft.  tunnel  at  Salida,  Colorado. 
At  Georgetown,  Colorado,  as  much  as  62  to  65  ft.  of  holes  have- 
been  put  in  in  7|  hours.  At  Ouray,  Colorado,  1329  ft.  of  7  X  7J 
ft.  tunnel  were  completed  in  11  months  at  a  cost  of  $13  per  ft. 
At  Idaho  Springs,  Colorado,  8  ft.  of  5  X  7  ft.  heading  per  day 
are  common. 

This  drill  will  do  similar  and  equal  work  to  the  standard  air 
drill,  and,  as  shown,  power  consumption  is  only  from  one-half  to 
one-quarter  as  great.  The  makers  state:  " Where  electric  power 
is  available  at  a  less  price  than  air  or  steam  power,  due  to  high 
fuel  cost;  where  high  altitudes  impair  the  efficiency  of  the  ordi- 
nary air  compressor;  where  pipe  lines  would  be  objectionable  in 
an  ordinary  air-drill  plant;  where  electric  distribution  of  power 
and  its  attendant  uses  and  advantages  are  a  controlling  factor, 
these  are  the  places  where  the  electric-air  drill  offers  the  best 
combination  of  maximum  work  output  with  minimum  cost." 


102  ROCK  DRILLS 

Disadvantages.  —  There  are  several  other  factors  that  limit  the 
sphere  of  usefulness  of  this  drill  in  underground  mining.  Theoret- 
ical engineers  profess  small  regard  for  the  benefits  derived  from 
the  ventilation  caused  by  the  exhaust  of  standard  air  drills,  and 
state  that  this  work  can  be  better  and  more  cheaply  done  by 
installing  special  machinery.  This  is  not  true  in  most  cases  in 
metalliferous  mines.  This  machine  would  not,  in  most  mines, 
be  used  in  ill-ventilated  ends  or  in  hot  workings  where  the  ice- 
cold  exhaust  air  of  the  ordinary  drill  is  a  stimulant  and  alone 
makes  working  conditions  bearable  in  many  cases.  Where,  as 
in  South  Africa,  it  pays  to  work  two  or  three  machines  in  one  face 
of  only  7  X  6  ft.,  this  drill  with  its  compressor  would  be  in  the 
way  and  would  retard  moving  broken  rock.  In  steep  stopes  it 
could  not  be  used,  but  in  flat  stopes  there  should  be  a  field  for 
the  operation  of  the  smaller  sizes.  Where,  however,  headings  are 
advanced  with  one  drill,  or  where  they  are  large  enough  to 
allow  of  two  such  drills  being  worked  together  and  where  arti- 
ficial ventilation  is  available  as  in  some  tunnel  or  adit  work,  then 
this  drill  should  prove  most  efficient. 

Am  DRILLS  vs.  ELECTRIC  DRILLS 

In  attempting  to  compare  electric  with  air  drills  one  can  only 
say  that,  for  mining  purposes,  there  does  not  seem  to  be  a  large 
field  open  for  them  in  competition  with  air  drills  under  ordinary 
conditions.  Their  use  might  be  recommended  in  places  where 
power  costs  are  very  high  and  where  high  altitudes  reduce  the 
efficiency  of  compressor  per  unit  of  air-cylinder  area;  where  con- 
ditions are  such  that  separate  artificial  ventilation,  or  efficient 
natural  ventilation,  would  have  to  be  provided,  regardless  of  the 
type  of  drilling  machine  employed;  where  labor,  as  in  Germany, 
for  instance,  is  cheap  and  efficient;  where  maximum  output  from 
any  face  is  not  the  chief  consideration;  where  the  rock  is  not  too 
hard  and  where  the  shorter  stroke  of  the  electric  piston  drill 
does  not  handicap  boring  speed  by  slow  ejection  of  the  broken 
particles.  For  instance,  an  electric  piston  drill  would  be  handi- 
capped putting  down  long  vertical  holes. 

Electric  drills  must  be  constructed  with  quick  running  shafts, 
fly-wheels,  and  gears.  On  the  surface,  electrical  machines  are 
carefully  kept  from  dust,  dirt,  and  water.  In  actual  mining  they 
must  work  constantly  exposed  to  these  drawbacks,  despite  care- 


ELECTRIC   DRILLS  103 

fully  contrived  covers.  Dynamos  and  their  insulation  are  on 
the  surface  guarded  from  jar  or  undue  stresses  of  any  kind,  and 
from  working  in  a  dusty  atmosphere.  In  mining,  they  are  mounted 
on  a  machine  whose  function  is  to  produce  jar  and  concussion. 
On  the  surface  such  machines  are  placed  in  the  hands  of  skilled 
certificated  mechanics.  Underground  they  must  be  left  to  the 
tender  mercies  of  the  man  whose  chief  tools  are  the  hammer  and 
the  drill. 

The  development  of  the  air-hammer  drill  has,  I  think,  prac- 
tically cut  off  the  chance  of  any  large  use  of  electric  drills.  They 
are  able  to  bore  more  rapidly,  are  simpler  and  lighter  than  any 
electric  drill ;  while  their  consumption  of  power  is  smaller  than 
that  of  a  piston  drill,  for  the  same  work,  in  certain  cases,  the 
ratio  of  power  developed  at  generator  to  power  exerted  on  the 
bottom  of  the  hole  will  almost  bear  comparison  with  that  of 
electric  drills.  The  Temple  electric-air  drill  should  also  limit  the 
sphere  of  usefulness  of  any  purely  electric  drill. 

Air  drills  have  one  great  advantage  over  electric  drills  in  that 
they  provide  ventilation  and  cool  the  working  place.  The  impor- 
tance of  this  in  modern  mining  is  not  always  realized.  Professor 
Henry  Louis  writes: 

"I  may  add  that  the  argument,  occasionally  put  forward  in 
favor  of  the  pneumatic  drill,  that  it  helps  to  ventilate  a  close  end, 
has  in  my  opinion  very  little  weight,  because  it  is  obviously  easy 
to  produce  any  desired  amount  of  ventilation  by  means  of  small 
electrically  driven  fans,  which  will  give  a  continuous  air  current, 
whereas  the  drill  does  not  supply  any  air  at  the  times  when  this 
is  most  needed,  that  is  to  say,  after  shots  have  been  fired,  and 
whilst  the  men  are  doing  their  hardest  manual  work  —  namely, 
setting  up  the  drill." 

It  is  true  that  the  drill  does  not  supply  air  after  shots  are 
fired;  but  it  is  no  less  true  that  rapid  development  work  on  the 
Rand,  for  instance,  would  be  impossible  if  the  same  air  hose 
that  worked  the  drill  were  not  there  to  blow  out  the  smoke  after 
blasting.  Any  one  who  knows  anything  of  the  difficulty  of  pro- 
tecting from  damage  by  blasting,  etc.,  our  system  of  small  pipes 
to  carry  air  under  high  pressure  in  mines  would  hesitate  before 
thinking  of  trying  to  put  in  large  pipes  to  carry  air  from  small 
electric  fans.  In  the  Rand  mines  the  air  pipes  get  blasted  often 
enough  as  it  is. 


104  ROCK  DRILLS 

Scott  Gasolene  Rock  Drill.  —  A  rock  drill  operated  entirely  by 
gasolene  has  been  designed  by  L.  L.  Scott,  Joplin,  Missouri.  In 
gene'ral  appearance  it  resembles  an  ordinary  air  drill.  The 
machine  operates  on  the  two-cycle  principle  and  the  mixed  air 
and  gas  is  drawn  in  at  the  upper  and  lower  ends  of  the  drill, 
through  ports  on  the  top  of  the  cylinder.  A  spark  plug  and 
timing  device  explode  the  charges  alternately  and  these  act  on 
the  inner  faces  of  the  pistons;  an  explosion  occurs  on  each  up- 
stroke -and  on,  each  down  stroke.  The  pistons  are  solid  steel 
castings,  the  upper  ends  being  connected  to  the  crank-shaft 
through  the  connecting  rod;  the  lower  ends  are  connected  by 
a  swivel  to  the  drill  rod.  The  cushions  are  in  the  interior  of 
the  lower  piston  and  the  rotating  mechanism  is  in  the  lower 
receiving  chamber.  In  this  drill  the  explosion  chambers  are  so 
arranged  that  the  heat  will  not  affect  the  rotating  device  or  drill 
rod. 

The  rotation  of  the  drill  rod  is  independent  of  the  piston. 
The  steel  is  held  by  the  usual  form  of  a  U-bolt  chuck  and  the  drill 
is  fed  by  an  ordinary  feed  screw.  In  the  oiling  system,  the  oil 
is  mixed  with  the  gasolene  and  the  mixture  is  sucked  in  with  each 
charge,  thoroughly  oiling  every  moving  part  of  the  machine. 


OPERATING  DRILLS  ON  THE  SURFACE  AND  UNDER- 
GROUND 


THE  first  consideration  of  both  supervisor  and  miner  must 
be  to  insure  a  plentiful  supply  of  tools  suitable  for  boring  the 
rock.  In  many  cases  anything  in  the  way  of  machines,  fittings, 
tools,  and  bits  is  deemed  good  enough  to  use. 

UNDERGROUND  DRILLING 

The  miner  should  be  furnished  with  a  rock  drill  adapted  to 
the  work  he  has  to  do ;  to  the  hardness  of  the  ground;  to  the  length 
of  hole  required;  also  with  a  bar  or  bars  of  such  lengths  as  to 
adapt  themselves  to  the  width  or  height  of  the  excavation  made. 
These  should  be  from  one  to  two  feet  shorter  than  the  hight  of 
working  place.  A  saddle,  a  clamp,  and  arm  should  also  be  pro- 
vided. 

Wedges  and  Blocks.  —  Wedges  and  blocks  for  securing  these 
bars  in  position  should  be  also  at  hand.  It  is  a  good  plan  to  make 
the  blocks,  Fig.  78,  of  large  size,  say 
14  in.  X  3  in.  to  7  in.  X  24  in.  for,  the 
foot  block  of  a  double  jack  bar,  and 
12  in.  X  3  in.  to  7  in.  X  7  in.  for  the 
top  block.  These  blocks  are  best  made 
of  hardwood  and  are  secured  against 
splitting  by  bolting  two  T\-in.  iron 
plates  on  their  opposite  sides  by  two 
bolts  across  the  grain  of  the  wood. 


FIG.  78.  —  Foot  block  with 
steel  plate. 


These  are  for  use  in  driving  levels  and  in  large  stopes;  other 
smaller  blocks  are  also  to  be  supplied  for  making  up,  and  for 
use  in  narrower,  steeper  places.  It  is  a  wise  plan  to  make  a 
fixed  issue  to  both  day  laborers  and  contractors  of  these  blocks 
and  wedges,  and  to  charge  for  any  excess  used  over  a  certain 
number;  only  in  this  way  is  waste  checked. 

Lockers  and  Tools.  —  The  miner  should  be  given,  also,  a  box 
in  which  to  keep  his  explosives  if  they  are  not  issued  to  him  at 

105 


106  ROCK  DRILLS 

every  firing;  also  a  small  box  for  detonators  and  a  large  box  to 
keep  fuse,  certain  spare  parts  of  his  machine,  his  oil  can  or  oiler, 
chuck  and  clamp  spanner,  Stilson  wrench,  •" shifting"  spanner 
and  a  few  hose  connections.  He  will  also  require  a  sufficient 
number  of  drill  bits  of  various  sizes,  sharpened  to  the  gage  and 
tempered  suitably  for  boring  the  rock  attacked. 

Pipe  Lines  and  Hose.  —  Water  must  be  provided,  preferably 
under  pressure  in  a  pipe  line,  following  the  air  line,  with  a  hose 
and  nozzle  so  that  a  jet  of  water  may  be  fed  into  the  hole  bored 
or  to  an  attachment  on  the  machine.  An  air  hose  of  the  right 
diameter  should  be  supplied  for  the  size  of  machine  used,  IJ-in. 
hose  being  the  minimum  size  for  a  3i-in  machine.  Care  should 
be  taken  that  the  hose  is  not  so  punctured  that  most  of  the  air 
escapes  before  reaching  the  rock  drill,  or  so  old  that  the  rubber 
lining  has  perished  or  curled  up,  stopping  the  passage  of  the  air 
at  a  right  pressure  through  it.  With  it  there  must  be  a  supply  of 
proper  fittings  and  gaskets  to  make  air-tight  connections  between 
hose  and  pipe  line,  and  hose  and  machine.  Pieces  of  mining 
fuse  cut  to  the  proper  length  make  an  efficient  packing.  These 
are  always  available  so  there  is  no  excuse  for  leaky  connections. 

Setting  Up.  —  The  miner  who  is  the  happy  possessor  of  all 
these  requisites  for  efficient  work  now  proceeds  to  erect  his  bar 
in  front  of  the  rock  face  to  be  bored.  Here  at  once  his  intelli- 
gence and  experience  are  called  into  play.  The  first  requisite  for 
successful  work  is  a  firm  base  from  which  the  rock  drill  may  de- 
liver its  blows  on  the  rock.  If  the  tripod,  bar,  clamp,  and  arm 
do  not  furnish  a  rigid  support,  every  rebound  from  the  blow 
delivered  tends  to  throw  the  machine  out  of  line;  this  causes 
the  drill  bit  on  the  next  blow  struck  to  extend  its  force  diagonally 
on  the  sides  of  the  hole  instead  of  on  the  bottom.  In  other  words, 
a  glancing  blow  is  struck  on  the  side  of  the  hole  instead  of  a  true, 
fair,  and  direct  blow  on  the  bottom  (Fig.  79).  The  hole  will 
be  bored  rifled;  the  bit  blunted;  the  machine  strained  and  the 
drill  bit  bent  or  broken;  finally  the  bar  itself  may  become  loosened 
and  will  fall. 

The  roof  and  floor  of  the  drive,  the  foot  and  hanging  wall  of 
stope,  or  the  sides  of  shaft  are  now  examined  for  two  surfaces  as 
nearly  parallel  as  possible  to  "rig,"  or  "set  up,"  the  bar  between 
them.  (See  Fig.  80  for  good  and  bad  "set-up.")  This  is  not  the 
only  consideration.  In  driving,  sinking,  or  stoping,  the  bar  must 


OPERATING   ROCK  DRILLS 


107 


be  placed  at  the  right  distance  from  the  face  so  that  when  the 
machine  is  erected  on  an  arm,  set  parallel  to  the  face,  or  on  the 
bar  itself,  the  first  or  starting  bit  will  be  about  touching  the  rock 
when  the  piston  is  drawn  out  and  the  machine  itself  run  back  in 
its  cradle.  This  will  insure  the  holes  being  as  far  as  possible 
bored  the  maximum  length  allowed  by  the  length  of  the  longest 


FIG.  79.  —  Dotted  line  shows  the  effect  of  excessive  vibration  of  arm  and  bar. 

bit,  and  that  the  minimum  amount  of  boring  will  be  done  with 
the  cylinder  run  far  out  of  its  cradle  where  it  has  more  play, 
with  less  guidance  given  to  the  blow.  It  is  very  hard  to  start 
or  pitch  a  hole  with  the  machine  run  out,  especially  if  the  guides 
be  worn.  On  the  other  hand,  the  machine  may  be  set  so  close 
to  the  face  that  drill  bits  are  hard  to  take  out  of  the  hole  past 
the  chuck  and  front  end  of  machine;  the  jig  bolt  of  the  machine 


Wedge* 


FIG.  80.  —  The  left  bar  cannot  slip  out.     The  position  at  the  right 
is  bad  —  a  slight  jar  will  tend  to  make  the  bar  slip  out. 

may  have  to  be  loosened  every  time  and  the  machine  swung  aside 
to  give  enough  room.     Thus  time  would  be  lost. 

The  rock  driller  has  yet  perhaps  the  most  important  matter 
to  consider  before  he  places  his  bar  in  position.  He  must  set  it 
up  so  that  he  can  bore  the  maximum  number  of  holes,  so  placed 
as  to  act  with  the  greatest  efficiency  in  breaking  the  rock  from 
the  one  rigging  up.  In  this  matter  experience  alone  can  enable 
the  workman  to  apply  theoretical  principles  to  actual  work. 


108 


ROCK  DRILLS 


Planning  Work. — A  skilled  workman  studies  the  whole  face. 
He  must  use  an  imagination  based  on  practical  knowledge  to 
judge  what  ground  a  certain  hole  will  break  and  how  much 
it  will  leave  for  another.  Unseen  heads  and  slips  in  the  rock  may 
make  his  calculation  more  or  less  wrong;  but  can  never  render 
it  useless.  It  is  the  possession  of  this  faculty  that  makes  all  the 
difference  between  a  good  and  bad  workman,  especially  in  hard, 
tight  ground.  When  a  workman  is  seen  time  after  time,  as  is 
only  too  common  in  certain  fields,  putting  in  his  second  hole  in 
such  a  position  that  the  explosion  of  the  first  hole  breaks  all  the 
burden  from  it,  while  he  always  gives  it  the  same  allowance  of 
explosive,  he  is  worse  than  useless  as  a  miner.  It  must  also  be 
remembered  that  a  large  piston  machine  will  be  at  work  actually 
boring  only  about  half  its  working  time.  The  rest  of  the  time 
will  be  taken  up  setting  up  machines,  moving  the  machine  to  a  new 
position  on  bar  or  arm,  or  changing  drill  bits,  etc.  Hence  the  miner 
plans  his  work  to  make  the  time  lost  in  setting  up  bear  as  small  a 
ratio  as  possible  to  the  total  working  time.  The  whole  face  will  be 
studied  and  every  hole  planned  out  beforehand.  The  place  where 
each  hole  will  be  started  or  " pitched"  is  decided  upon;  its  direc- 
tion and  depth  considered,  and  the  relative  position  of  the  machine, 
bar  and  arm,  to  bore  the  required  holes,  is  planned  out. 

The  bar  is  then  set  up  in  the  best  situation  in  regard  to  the 
matters  mentioned.  This  right  placing  of  the  bar  is  especially 

important  in  stoping  narrow 


reefs  in  hard  and  tight  ground. 
In  the  case  of  a  flat  or  inclined 
stope,  as  shown  in  Fig.  81,  the 
direction  of  the  holes  should  be 
parallel  to  the  free  face  and 
placed  in  the  way  shown.  Here 
there  is  only  one  right  position 
for  the  bar  in  order  that  the 
holes  may  be  bored  against  the 
bar  and  at  the  extremity  of 
the  arm,  alternately.  A  careless  set-up  means  a  spoilt  bench; 
while  on  a  narrower  bench,  where  only  two  or  three  holes  can  be 
bored  to  advantage,  the  bar  now  would  be  best  set  as  shown  in 
Fig.  82,  so  that  all  holes  will  be  bored  from  one  side  of  the  bar, 
saving  time  in  turning  the  arm  and  machine  round  the  bar. 


FIG.  81.  —  Showing  correct  position  of 
the  arm  for  drilling  holes  parallel 
to  the  free  face. 


OPERATING  ROCK   DRILLS  109 

In  a  winze,  raise,  or  drive,  the  position  of  the  bar  will  be  about 
the  center  of  the  face  unless  holes  are  to  be  drilled  towards  some 
wall  or  seam.  Each  case  calls  for 
separate  consideration,  and  when 
a  tripod  is  used  the  same  prin- 
ciples  apply.  The  object  must 
always  be  to  bore  as  many  holes 
as  possible  from  one  "rig  up,"  to 
break  the  ground  with  the  fewest 
possible  number  of  holes,  and  to  FIG.  82.  —  Position  of  bar  and  arm 
avoid  taking  up  more  of  the  ac-  when  ^^  a  narrow  bench- 
tual  working  time  in  rigging  up  and  moving  machine  than  is 
necessary. 

Bars.  —  Either  single- or  double-jack  bars  are  used.  Double- 
jack  bars,  as  before  explained,  have  two  tightening  screws  at 
one  end.  These  are  generally  used  in  flat  stopes,  raises,  and  in 
driving.  In  some  cases  the  double  jack  is  made  separate  from 
the  bar  itself,  two  screws  being  fixed  to  a  block  of  wood,  and  a 
bar  used  without  any  screw  on  it  at  all.  Generally,  however, 
the  screws  are  set  in  a  steel  frame  fixed  to  the  bar. 

The  double-jack  bar  is  always  set  so  that  the  line  of  the  jacks 
and  the  blocks  used  are  in  the  direction  of  boring,  otherwise  they 
interfere  with  the  arm  and  machine  when  holes  are  being  bored 
low  down.  The  bar  is  then  placed  between  the  blocks;  wedges 
are  driven  between  blocks  and  the  rock  until  the  bar  is  slightly 
wedged.  The  blocks  at  each  end  have  their  faces  kept  parallel 
to  the  faces  of  the  ends  of  the  bar  as  far  as  possible.  Where  a 
double-jack  bar  is  used  the  ends  of  the  double  screws  are  placed 
in  cast-iron  feet  which  distribute  the  pressure  over  the  face  of 
the  blocks.  It  is  a  good  plan  to  get  these  feet  bored  out  and 
secured  together  by  a  piece  of  chain  about  18  in.  long  before 
they  are  sent  down  the  mine.  They  are  thus  not  so  easily  lost. 
The  bar  is  now  extended  by  means  of  its  screw  or  the  screws  of 
the  jack.  This  is  done  gently  at  first  until  its  ends  grip  the 
block  firmly.  Then  a  jack  bar,  which  is  a  piece  of  steel  of  1J— 
in.  or  IJ-in  diameter,  with  suitable  ends  to  go  into  the  capstan 
heads  of  the  screws,  is  inserted;  the  screws  are  pulled  and  ham- 
mered round  until  the  bar  forms  a  rigid  column  between  the  rock 
walls  or  between  the  timbers  of  a  square  set  which  have  been 
pioperly  braced  to  take  the  pressure.  Miners  must  be  pro- 


110  ROCK  DRILLS 

vided  with  special  jack  bars  for  this  work,  otherwise  the  shanks 
of  drill  bits  will  be  used,  thus  bending  and  breaking  them. 

Setting  the  Machine.  —  Even  after  the  bar  has  been  tightened 
to  its  apparent  limit,  it  will  require  further  attention  shortly 
after  the  machine  has  started  working,  and  even  if  locked  by  the 
set  screw  will  repay  attention  during  work.  The  screws  on  the 
double  jack  are  locked  in  position  by  driving  f-in.  bars  through 
the  capstan  heads  and  against  the  bar  itself,  one  on  either  side. 
Serious  accidents  have  happened  owing  to  operators  starting  their 
machine  at  full  power  before  satisfying  themselves  that  the  bar 
is  firm.  Where  an  arm  is  employed,  as  it  sometimes  is  in  a  steep 
stope,  fixed  to  a  horizontal  bar,  the  extra  leverage  given  to  the 
weight  and  rebound  of  machine  is  most  severe  on  the  bar.  When 
a  vertical  bar  is  used  with  arms  a  small  collar  is  now  fixed  on  the 
bar  to  support  the  arm  at  the  hight  suitable  for  boring  the  first 
hole.  The  arm  is  then  placed  on  the  bar  and  tightened  up.  The 
"clamp,"  "saddle,"  or  "seat"  for  the  machine  is  then  placed  in 
the  proper  position  on  the  arm  and  fixed  there  not  too  tightly. 
It  now  remains  to  get  the  machine,  which  may  weigh  300  lb.,  into 
its  seat  in  the  clamp.  To  lift  this  weight  to  a  hight  of  3  or  5  ft. 
and  to  place  it  in  the  clamp  would  require  a  great  expenditure 
of  brute  strength.  There  are  several  tricks  to  avoid  this.  Where 
there  is  head  room,  as  in  shaft  sinking,  a  starter  drill  bit  is  first 
placed  in  the  machine  and  the  machine  up-ended  on  its  bit  until 

it  stands  nearly  vertically  against 
the  bar  or  arm,  which  has  the  clamp 
fixed  with  its  seat  vertical  (Fig.  83). 
The  feed-screw  of  the  machine  is 
then  run  out  until  the  neck  and  seat 
of  the  cradle  is  raised  opposite  the 
seat  of  the  clamp,  which  has  its  jig 
FIG.  83.-AUaching  drill  to  bolt  slackened  off.  It  then  slips  in 

without  effort;   the  jig-bolt  clamp  is 

secured,  and  using  the  arm  and  clamp  as  a  fulcrum,  the  machine 
can  easily  be  swung  into  a  horizontal  or  other  position  and  every- 
thing tightened  up.  In  other  situations  a  tackle  slung  from  the 
timber  may  be  used,  or  in  an  inclined  stope  the  machine,  always 
with  a  starter  to  make  handling  more  easy,  is  slid  from  higher 
up  the  slope  on  to  the  bar  (Fig.  84). 

Oiling.  —  The  miner  having  his  machine  in  the  clamp,  with 


OPERATING   ROCK  DRILLS  111 

jig  or  clamp  bolt  sufficiently  tightened  to  hold  it,  will  now  oil 
his  machine,  remembering  that  a  teaspoonful  of  the  best  oil  put 
in  before  every  hole  is  bored,  or  oftener,  is 
the  only  proper  way  to  keep  the  machine 
working  freely,  if  oil  is  not  supplied  auto- 
matically. The  idea  of  most  miners  seems 
to  be  to  give  the  largest  possible  doses  with 
the  longest  possible  interval  between  them. 
Oil  should  not  be  poured  down  rubber  hose. 

Hose  Connections.  —  The  hose  is  first 
attached  to  the  pipe  line,  and  the  cock  on  the  end  of  pipe  turned 
on  a  moment  to  throw  any  grit  out  that  may  have  entered  since 
the  hose  was  last  in  use.  The  air  cock  of  the  machine  is  then 
turned  off  and  the  hose  attached  to  the  spud  on  the  machine. 
If  rubber  rings  are  not  available  for  packing  joints,  fuse  is  always 
at  hand  and  makes  a  satisfactory  packing.  No  leaks  should  be 
allowed  at  any  joint. 

Starting  the  Machine.  —  The  .clamp  and  jig  bolts  are  then 
loosened  sufficiently  to  allow  the  machine  to  be  placed  in  position 
to  start  the  first  hole.  Before  starting  holes  all  bolts  are  care- 
fully tightened  and  the  starter  secured  in  the  clutch  by  the  bolts 
or  wedges  used.  With  the  old-fashioned  taper  chuck,  now  rapidly 
going  out  of  use,  no  tightening  was  necessary  as  the  bit  tight- 
ened itself  on  striking  the  rock.  The  piston  is  pulled  out  to  its 
full  extension,  if  possible,  and  the  machine  fed  forward  by  turn- 
ing the  feed-screw  until  the  bit  touches  the  rock;  air  is  then  turned 
on  very  gently  until  the  piston  reciprocates  and  the  bit  begins 
to  strike  the  rock.  The  stroke  is  then  shortened  by  feeding  the 
machine  forward  and  more  air  turned  on. 

In  starting  a  hole  in  hard  rock  full  stroke  and  full  air  are  not 
used  until  the  hole  reaches  a  depth  equal  to  the  stroke  of  the  ma- 
chine. In  soft  ground  full  speed  and  full  stroke  can  often  be  used  as 
soon  as  the  operator  is  certain  everything  is  tight  and  firm.  If  the 
surface  to  be  bored  is  not  at  right  angles  to  the  drill  bit,  a  true 
surface  may  in  some  cases  be  cut  out  with  a  short  gad  or  pointed 
chisel  or  formed  by  chipping;  but  in  really  hard  rock  it  may  be 
necessary  to  start  a  hole  with  the  position  of  the  machine  differ- 
ent from  that  used  when  boring  in  the  direction  required.  Sup- 
pose we  have  a  face  like  the  one  shown  in  plan,  Fig.  85,  with  a 
hole  required  at  A  to  go  in  the  direction  shown.  The  bar  has 


112  ROCK   DRILLS 

to  be  in  position  B  to  bore  the  rest  of  holes  to  best  advantage. 

If  an  attempt  be  made  to  start  with  machine  or  the  arm  against 
B,  to  bore  the  hole  in  hard  ground,  the  bit 
will  at  every  stroke  glance  away  in  the  direc- 
tion shown,  laying  severe  bending  stresses  on 
the  piston  guides,  clamp,  and  seat  of  the 
machine;  tending  to  break  the  drill  bit  at  the 
shank  and  probably  merely  grooving  the  rock 
in  a  direction  along  its  face  away  from  the 
machine.  Time  is  thus  lost;  drill  bits  are 
blunted,  and  the  machine  stressed  for  no  re- 

FIG.  85. — Starting  a     suit.     Sometimes  it  is  not  at  once  apparent 

face  ^  ^  °bUqUe  to  the  beSmner  and  others,  not  even  those 
who  are  supposed  to  be  skilled,  that  this  action 
is  being  set  up;  but  the  intense  vibration  set  up  should  at  once 
be  noticed  and  its  cause  sought.  If  the  machine  be  placed  first 
in  position  D,  the  drill  bit  will  strike  the  rock  squarely  and  a  hole 
about  4  in.  deep  can  be  rapidly  bored.  The  machine  is  then 
undamped,  moved  back  to  position  B;  the  drill  bit  has  a  ledge 
to  start  cutting  on  and  the  hole  can  be  bored  in  the  direction 
required. 

Old  Holes.  —  The  operator  must,  before  starting  any  hole, 
satisfy  himself  that  it  is  not  in  the  vicinity  of  any  old  hole.  If 
it  is,  the  ground  will  generally  be  found  so  broken  near  it  that 
the  new  hole  will  "run  away"  into  the  old  hole.  He  must  not 
bore  in  any  old  hole  unless  he  has  been  able  to  make  himself  quite 
certain  that  there  is  no  possibility  of  any  explosive  being  in  its 
vicinity.  To  do  this  he  must  be  able  to  see  the  bottom  of  the 
hole  and  remove  all  shattered  rock.  Cases  have  occurred  where 
an  old  hole  has  been  apparently  free  from  any  portions  of  unex- 
ploded  powder,  yet  in  drilling  in  them  an  explosion  has  occurred, 
due  to  portions  being  driven  into  a  crack  or  crevice,  or  owing  to 
nitroglycerine  having  leaked  out  into  the  broken  rock  around  the 
hole.  Some  cases  have  occurred  on  the  Rand  where  a  white 
supervisor  has  first  drilled  a  little  in  an  old  hole,  and  then,  satis- 
fied that  there  was  no  danger,  has  set  a  native  to  drill,  when, 
some  time  later,  an  explosion  has  occurred.  Drilling  in  the 
sockets  of  old  holes  is  in  many  countries  forbidden  by  law;  but 
every  practical  miner  knows  that  cases  occur  where  it  is  impos- 
sible to  avoid  doing  this.  Any  one  who  drills  in  an  old  hole, 


OPERATING  ROCK   DRILLS  113 

the  bottom  of  which  he  cannot  properly  examine,  takes  his  life 
and  the  lives  of  others  in  his  hand.  The  miner  must  also  be  care- 
ful to  see  that  his  hole  does  not  run  into  any  old  hole  in  depth. 
In  some  stopes  there  might  be  3  ft.  or  more  of  an  old  hole  which 
had  failed  to  explode  with  the  previous  blast;  and  accidents  due 
to  boring  into  these  are  only  too  frequent. 

Drilling  in  Hard  Ground.  —  Starting  and  drilling  a  hole  in 
hard  and  soft  ground  are  very  different  matters.  I  have  seen 
miners  from  soft  rock  mines  completely  at  a  loss  when  asked  to 
drill  in  really  hard  rock.  To  drill  in  such  ground  requires  the 
closest  attention  on  the  part  of  the  miner.  In  starting  the  hole 
constant  watch  has  to  be  kept  that  the  corners  are  not  worn  off 
the  starter  bit  to  such  an  extent  that  the  hole  is  of  too  small  a 
diameter  for  the  next  drill  to  follow;  also  that  none  of  the  fol- 
lowing sizes  become  worn  away  or  broken  with  a  like  inconvenience. 
Excessive  blunting  of  the  bit  has  another  bad  result,  as  it  causes 
breakage  and  bending  of  steel  and  jars  the  machine.  A  drill 
bit,  no  matter  how  hard  the  ground  and  how  high  the  air  pres- 
sure, will  rarely  bend  or  break  as  long  as  it  keeps  a  cutting  edge; 
but  as  soon  as  it  begins  to  thump  the  rock,  trouble  ensues.  An 
experienced  operator  boring  in  hard  rock  places  his  hand  on  the 
steel  while  the  drill  is  working,  and  can  tell  by  the  sound  and 
feel  if  it  be  excessively  blunted  or  not. 

For  boring  hard  ground,  the  steel  supplied  must  be  of  short 
following  lengths,  as  a  bit  cannot  be  expected  to  drill  more  than 
12  or  15  in.,  often  much  less  than  that.  As  soon  as  the  hole 
is  started,  if  it  be  in  a  downward  direction,  water  is  splashed  into 
it  and  enough  always  kept  in  it  to  allow  the  drill  to  "spit"  or 
eject  the  broken  fragments  in  splashes  of  dilute  mud.  In  soft 
rock,  in  both  dry  and  wet  holes,  the  drill  may  cut  faster  than  it 
can  eject  the  cuttings.  In  such  cases  the  stroke  should  be  kept  at 
its  longest  and  part  of  the  air  turned  off.  If  the  drill  steel  is  not 
running  freely  or  turning  properly,  three  things  may  be  wrong: 

The  drill  may  be  bent,  especially  at  the  shank,  thus  causing 
the  bit  to  strike  and  rub  against  the  sides  of  the  hole. 

The  hole  may  have  run  away  on  some  hard  or  soft  head  in 
the  rock,  causing  the  steel  to  bind  against  one  side  of  the  hole. 
To  remedy  this  the  jig  and  clamp  bolt  are  loosened  and  the 
machine  moved  to  one  side;  if  necessary,  the  arm  is  also  raised 
or  lowered. 


Ill  ,      ROCK  DRILLS 

In  ground  with  hard  heads,  or  streaks,  on  which  the  bit  tends 
to  glance  off  or  bind  on  the  bottom  of  hole,  it  is  sometimes  help- 
ful to  place  pieces  of  hard  rock  or  even  small  pieces  of  iron  in  the 
hole  and  run  the  drill  with  a  short  stroke  for  a  time;  thus  the  bit 
gets  a  chance  to  establish  a  landing  on  the  hard  ledge  and  to  enter 
it.  When  drilling  a  dry  hole  with  a  small  elevation,  the  broken 
rock  tends  to  accumulate  on  the  bottom  of  the  hole  and  to  force 
the  boring  tool  upward.  In  such  case  it  is  frequently  necessary 
to  lower  the  arm. 

The  third  trouble  may  be  that  the  ratchet  and  turning  arrange- 
ments of  the  drill  itself  are  out  of  order.  This  can  be  ascer- 
tained generally  by  turning  the  chuck  by  hand.  The  machine 
may  need  only  oiling  in  some  cases.  With  wet  holes  too  much 
water  is  as  bad  as  too  little,  as  the  splash  is  thereby  reduced  too 
much.  In  dry  holes  a  constant  stream  of  cuttings  should  run  from 
the  hole.  When  boring  with  solid  steel  the  hole  should  be  scraped 
out  fairly  often.  The  air  should  be  turned  off  until  the  drill  just 
reciprocates  and  the  machine  runs  right  back  on  its  feed-screw; 
this  helps  the  travel  of  the  cuttings  towards  the  mouth  of  hole. 

Changing  Drill  Bits.  —  As  soon  as  one  drill  is  run  out  to  its 
full  length,  or  when  it  is  judged  to  be  blunted,  the  air  is  turned 
off.  While  the  machine  is  being  screwed  back  the  bolts  of  the 
chuck  are  loosened  by  one  of  the  operators  so  as  to  lose  as  little 
drilling  time  as  possible.  The  drill  is  then  withdrawn  past  the 
front  head  and  chuck  of  the  machine.  When  a  long  drill  is  being 
used  and  the  machine  is  set  up  close  to  the  face,  difficulty  may 
occur  in  doing  this  and  in  inserting  a  larger  one  in  the  hole.  To 
render  this  easier,  the  jig  bolt  of  the  machine  is  loosened  and  the 
machine  swung  on  one  side.  With  a  machine  using  solid  steel, 
the  drilling  of  holes  in  a  true  horizontal  direction  or  a  few  degrees 
above  must,  if  possible,  be  avoided,  as  it  is  a  tedious  and  heart- 
breaking work.  Special  steel  such  as  that  shown  in  Fig.  107 
should  be  used. 

Blasting.  —  The  tendency  of  the  average  miner  is  to  drill  too 
few  holes  for  the  work  required  in  breaking  the  face  in  develop- 
ment. This  causes  bad  work,  loss  of  time,  and  disappointment. 
It  is  only  the  expert  who  understands  something  of  the  theory 
of  blasting  who  can  begin  to  economize  in  drilling  and  in  the 
use  of  powder.  The  beginner  does  well  to  put  in  an  extra  hole 
in  all  doubtful  cases.  All  the  factors  to  be  considered  in  the 


OPERATING  ROCK   DRILLS  115 

work  of  breaking  ground  can  be  best  learned  by  one  who  has 
to  start  with  some  knowledge  of  the  theory  of  the  subject: 
but  this  knowledge  must  be  supplemented  by  plenty  of  actual 
practical  experience.  When  all  necessary  holes  have  been  drilled, 
the  machine,  arm,  and  bar  are  taken  down  and  placed  in  a  place 
of  safety.  In  doing  this,  care  must  be  exercised.  The  detonation 
of  modern  high  explosives  releases  an  immense  volume  of  gas,  and 
the  blast  from  a  heavily  charged  hole,  or  holes  forming  a  cut,  is 
most  powerful  and  does  damage  only  to  be  believed  by  those  who 
have  seen  the  effects  wrought.  Often  a  machine  or  gear  may  be 
moved  by  the  blast  of  a  shot  going  off  first,  or  have  its  covering 
of  rocks  or  planks  removed  and  then  be  damaged  by  rocks  from 
a  second  shot. 

After  removing  machine  and  gear,  the  holes  are  cleared  of 
mud  and  water.  This  may  be  done  by  a  blow  pipe,  which  in  min- 
ing consists  of  a  suitable  length  of  f-in.  or  1-in.  pipe,  having  a 
right-angle  bend  about  18  in.  long,  on  one  end,  to  serve  as  a  handle. 
The  end  of  the  pipe  on  this  bend  is  provided  with  a  spud  to 
attach  it  to  the  air  hose.  Holes  may  also  be  cleaned  out  in 
the  manner  described  in  the  section  on  the  use  of  machines  in 
shaft  sinking,  or  by  the  use  of  a  pipe  having  a  ball  valve  at  the 
bottom,  or  even  by  a  proper  sized  wooden  rammer.  With  high 
explosives,  a  little  water  or  loose  mud  in  a  hole  is  rather  an 
advantage,  as  it  displaces  any  air  between  the  cartridges  and 
acts  as  tamping. 

Starting  a  Steam  Drill.  —  When  working  with  steam  instead 
of  compressed  air  several  precautions  have  to  be  taken  into  con- 
sideration. A  little  steam  must  be  admitted  and  then  shut  off;  the 
piston  worked  by  hand  a  few  times  to  insure  that  all  the  parts 
of  machine  are  evenly  heated  and  expanded.  The  side  rods  are 
first  loosened,  and  only  tightened  up  when  the  machine  is  warmed. 
These  rods  should  never  be  made  too  tight  as  they  are  liable  to 
break  at  any  time  if  too  much  stress  is  put  upon  them.  It  is 
generally  necessary  to  screw  a  special  pipe  into  the  exhaust  to 
take  the  exhaust  stream  far  enough  away  so  that  it  will  not 
impede  the  workmen.  The  drill  is  not  oiled  until  the  condensed 
steam  in  pipes  and  passages  has  been  blown  out. 

Working  a  Drill  with  a  Tripod.  —  A  drill  is  worked  on  a  tripod 
where  there  are  no  side  walls  or  roof  available  to  set  up  a  bar. 
It  is  often  useful  underground  in  cutting  large  chambers,  sinking 


116  ROCK  DRILLS 

shafts,  and  in  underhand  stopes .  It  is,  however,  chiefly  employed 
in  quarries  and  railway  cuttings. 

Before  erecting  the  tripod,  all  loose  earth  and  broken  rock 
must  be  removed.  If  there  is  much  of  this  work  to  do  it  will 
pay  to  employ  a  special  gang  to  prepare  the  blasting  spots.  The 
place  having  been  chosen  for  the  proposed  hole,  the  tripod  is  set 
up.  Small  holes  or  hitches  are  cut  in  the  rock  to  prevent  the 
legs  spreading.  Where  the  ground  is  of  such  a  character  that 
the  legs  gradually  settle  through  it,  wooden  blocks  may  be 
employed,  having  washers  or  iron  plates  with  holes  punched  in 
them  to  form  a  holding  or  socket  for  the  point  of  the  leg.  When 
the  legs  are  fixed,  the  saddle  is  placed  as  nearly  horizontal  as 
possible,  tightened  up  and  the  weights  put  in  position.  The 
machine  is  put  in  the  clamp  or  saddle,  fastened,  and  is  ready  for 
work. 

The  running  of  the  machine,  i.e.,  the  feeding  of  it  forward  to 
give  the  correct  length  of  stroke,  can  be  learned  only  by  practice. 
If  the  handle  is  not  turned  quickly  enough  to  feed  the  cylinder 
forward,  as  the  drill  bits  cut  the  rock,  the  piston  strikes  on  the 
cylinder  end,  and  if  allowed  to  do  this  often,  or  too  violently,  a 
side  rod  will  be  broken.  The  short  stroke  is  used  when  meeting 
with  a  head  or  when  the  bit  shows  tendency  to  stick,  and  in  start- 
ing a  hole.  The  beginner  must  not  be  distressed  if  the  drill 
sticks  occasionally;  it  is  only  repeated  sticking  and  refusal  to 
rotate  which  indicate  that  something  is  wrong.  Most  makes  of 
drills  will  stick  occasionally.  A  blow  from  a  hammer,  delivered 
on  the  drill,  near  the  hole,  will  in  such  cases  start  the  drill  .off 
again. 

Hints  for  the  Operator.  —  The  operator  should  make  himself 
acquainted  with  the  design  and  construction  of  each  part  of  the 
machine  used  by  him;  only  in  this  way  can  he  intelligently  work 
it  and,  if  necessary,  save  time  by  doing  small  repairs  and  replace- 
ments himself,  on  the  spot. 

This  knowledge  may  be  gained  partly  from  books,  but  it  can 
always  be  acquired  by  a  few  hours  spent  in  the  company  of  the 
mechanic  who  has  charge  of  the  repairs  to  machines  on  any  mine 
or  undertaking.  A  little  care  in  oiling  frequently,  and  in  stopping 
both  air  chest  and  exhaust  openings  with  a  piece  of  cloth  or  waste 
as  soon  as  work  is  finished,  will  amply  repay  themselves,  especially 
if  work  is  being  performed  on  contract.  If  the  valve  sticks,  do 


OPERATING  ROCK  DRILLS  117 

not  strike  the  valve  chest,  but  spend  a  few  minutes  in  taking  it 
off  carefully  and  examine  it  for  grit  or  other  things  in  the  air 
chest,  air  ports,  or  auxiliary  valve  or  valves. 

Above  everything  the  operator  should  himself  take  an  intelli- 
gent interest  in  the  condition  of  his  machine.  Even  the  best 
system  of  inspection,  which  is  usually  absent,  will  not  take  the 
place  of  a  man  who  takes  a  pride  in  keeping  his  tools  and  machine 
in  good  order.  Watch,  above  all,  for  worn  bushing  in  your  chuck, 
and  for  bent  jumpers,  as  they  mean  doing  your  work  twice  over. 
If  the  piston  starts  knocking  the  back  plate,  see  that  the  fitter 
re-bores  the  valve  chest.  If  you  work  on  contract,  tip  the 
rock-drill  fitter  and  the  blacksmith;  they  will  then  see  that 
you  get  your  machines  repaired;  that  you  get  the  drills  you 
need,  and  the  lengths  you  require.  Remember  also  that  it  is 
as  much  against  your  interest  as  the  company's  to  work  with 
a  leaking  air  hose  or  connections.  An  inch  hose  does  not,  at 
best,  supply  the  air  it  should  to  a  3j-in.  machine.  Every  cubic 
foot  of  air  loss  in  leakage  means  so  many  less  blows  struck  per 
minute. 

Old  miners,  when  boring  in  hard  ground,  having  lost  the 
gage  of  their  hole  and  cannot  get  another  bit  to  follow,  will  some- 
times swing  the  machine  out  of  position  and  explode  a  small 
charge  of  gelatine  in  the  hole  to  enlarge  it.  The  operator  can 
do  this  if  he  likes,  but  he  must  remember  that  the  risk  is  far  too 
great,  and  in  the  long  run  such  practices  are  paid  for  by  men's 
lives.  The  miner  must  take  risks;  but  this  is  not  a  fair  one. 
Many  accidents  have  occurred  through  trying  to  force  dynamite 
or  blasting  gelatine  into  a  hole  slightly  too  small,  owing  to  excess- 
ive wear  on  the  bits  used.  The  miner  is  anxious  not  to  lose  the 
result  of  his  shift's  work  and  he  uses  more  and  more  force 
until  one  day  an  explosion  occurs.  In  such  a  case,  if  mod- 
erate pressure  on  the  end  of  a  wooden  tamping  rod  will  not 
dislodge  the  cartridge,  put  in  about  half  a  cupful  of  water, 
allowing  it  to  stand  for  a  few  minutes.  In  nine  cases  out  of  ten 
it  will  be  found  that  it  has  soaked  the  paper  enclosing  the  cart- 
ridge and  lubricated  the  sides  of  the  hole  so  that  the  paper  tears 
and  gives;  the  cartridge  will  then  go  home  easily.  If  it  will  not 
go  right  in  the  water  soaking  past,  the  water  forms  a  tamping 
instead  of  the  air,  and  the  force  of  the  blast  is  not  lost  to  such 
a  great  extent. 


118 


ROCK   DRILLS 


LUBRICATING  DEVICES  FOR  ROCK  DRILLS 

There  is  great  need  for  a  thoroughly  satisfactory  automatic 
lubricator  for  piston  rock  drills.  In  the  Sergeant  drills  there  is, 
in  the  valve  chest,  a  spring  loaded  ball  valve  through  which  the 
machine  may  be  oiled  when  the  air  is  turned  off.  On  other  ma- 
chines there  are  holes  in  valve  chest  and  in  ratchet  box,  closed 
by  studs.  What  is  required  is  a  lubricator  that  is  part  of  the  ma- 
chine itself,  yet  not  taking  up  too  much  room,  and  at  the  same 
time  strong  enough  so  that  it  might  not  be  damaged.  Such  a 
lubricator  must  feed  oil  in  small  charges  over  regular  intervals 
while  the  machine  is  at  work.  On  the  Chicago  Giant  drill  there 


FIG.  86.  —  Lubricator  for  air  drill. 

is  a  device  shown  (Fig.  9)  attached  to  valve  chest;  but  with  what 
success  it  has  met  I  do  not  know.  The  same  company  also  manu- 
facture the  oiler  shown  in  Fig.  86,  for  attachment  to  air  hose. 

The  Chicago  Pneumatic  Tool  Company,  Chicago,  Illinois,  is 
supplying  an  independent  rock-drill  oiler  which  may  be  attached 
to  the  hose  connections  by  using  a  standard  nipple  and  tee  joint. 

The  upper  part  of  the  oiler  body  is  made  to  form  a  reservoir 
for  the  oil,  and  is  of  sufficient  capacity  to  hold  from  50  to  60 
oilings,  which  are  measured  out  to  the  drill  by  turning  a  star 
wheel.  One  filling  of  the  reservoir  chamber  will  last  a  day's  run. 

The  device  is  constructed  so  that  at  each  quarter  turn  of  the 
star  wheel  a  definite  quantity  of  oil  is  delivered  and  passes  into 
the  drill  with  the  operating  fluid. 


OPERATING  ROCK  DRILLS  119 

The  positions  of  the  arms  on  the  star  wheel  and  the  measur- 
ing pockets  in  oiler  coincide,  and  provision  is  made  for  automati- 
cally latching  at  each  quarter  turn  of  the  star  wheel. 

A  strainer  in  the  mouth  of  the  filling  chamber  prevents  dust- 
and  grit  from  being  introduced  with  the  oil.  This  strainer  is 
easily  removed  for  cleaning  . 

The  addition  of  one  teaspoonful  of  flake  graphite  to  each 
pint  of  oil  will  be  found  to  be  very  beneficial.  The  graphite  and 
oil  should  be  mixed  as  thoroughly  as  possible  before  placing  in 
the  oiler. 

George  Leyner  had  a  similar  device  also  for  hammer  drills. 
The  objections  to  them  are  that  oil  is  not  good  for  the  rubber 
linings  of  the  hose;  that,  with  unskilled  or  careless  labor,  the  ap- 
paratus may  be  left  on  the  pipe  line  and  blasted,  or  be  damaged 
by  trucks  or  shovelers.  George  Leyner  claims,  now,  to  have 
developed  an  efficient  oiler  for  his  large  hammer  drill.  The 
automatic  oiler  for  the  Gordon  drill  may  also  be  noted.  In 
Stephens  Climax  drill  lubrication  has  been  attempted  by  means 
of  a  stiff  lubricant  and  a  lubricator  like  Staffaeur's.  Claude  T. 
Rice1  thus  describes  the  Western  lubricating  valve,  Fig.  87: 

"There  is  great  need  for  an  efficient  lubricator,  continuous 
or  intermittent,  attached  to  the  drill  or,  better  still,  incorporated 
in  its  design.  As  the  speed  of  movement  and  number  of  strokes 
increases  as  the  use  of  hammer  drills  increases,  the  need  of  a  con- 
tinuous lubricator  or  oiler  also  becomes  greater.  It  seems  to 
me  that  this  is  the  direction  for  immediate  advance  in  drilling 
practice  rather  than  ultra-refinements  in  interior  design  of  the 
valves,  ports,  and  cylinders.  It  appears  that  in  view  of  this  need 
a  useful  adjunct  to  the  machine  drill  will  be  found  in  the  Western 
lubricating  valve,  which  I  do  not  hesitate  to  describe,  although 
I  have  never  seen  it  in  operation.  I  am  informed  that  this  valve 
has  been  used  by  the  Granite  Gold  Mining  Company,  at  Victor, 
Colorado,  for  more  than  six  months,  and  D.  L.  McCarthy,  the 
superintendent,  says  that  it  has  proved  satisfactory  in  every 
respect;  that  the  drill  is  kept  lubricated  under  all  conditions;  and 
that,  while  the  drill  is  running,  the  valve  remains  in  whatever 
position  that  it  is  turned  by  the  machineman,  which  is  a  strong 
recommendation  for  the  use  of  this  valve  on  one-man  machines. 

"It  is  an  internal-pressure  valve,  conical  in  shape,  which  fits 
1  Eng.  and  Min.  Journ.,  April  11,  1908. 


120 


ROCK  DRILLS 


into  a  barrel  that  is  surrounded  by  the  oil  reservoir.  The  valve 
plug  and  the  barrel  have  ports  which  register  when  the  valve  is 
closed,  and  air  is  then  admitted  to  the  top  of  the  oil  reservoir. 


FIG.  87.  —  Western  lubricating  valve  mounted  on  a  small 
piston  drill.     Also  section  of  same. 

Another  duct  leads  from  the  bottom  to  a  groove  in  the  valve 
plug.  This  groove  in  the  plug,  when  the  valve  is  opened,  connects 
with  the  main  air-way  of  the  valve  at  both  its  ends,  so  that  the 
oil  is  forced  out  into  the  air-way,  and  is  then  carried  by  the  air 
into  the  drill.  The  opening  of  the  valve  clqses  the  connection 
of  the  main  air-way  and  the  groove  with  the  oil  reservoir.  The 


OPERATING   ROCK   DRILLS  121 

valve  thus  becomes  an  intermittent  lubricator,  which  oils  the 
machine  every  time  that  the  air  is  turned  on  and  off.  As  the 
air  is  shut  off  frequently  in  drilling  in  order  to  change  drills,  to 
clean  out  the  hole,  etc.,  lubrication  is  frequent  enough  to  be  effi- 
cient. 

"This  valve  has  also  other  merits,  for  it  has  two  swivel  joints, 
one  where  the  hose  is  connected,  and  one  where  the  valve  is  con- 
nected to  the  drill." 

I  have  tried  this  valve  in  South  Africa,  but  find,  for  work  in 
a  drift  where  two  machines  are  in  use  on  one  bar,  with  unskilled 
labor,  that  it  projects  too  much  from  the  machine.  Besides  this, 
all  drills  in  use  here  lead  the  hose  directly  from  the  rear  of  the 
valve  chest,  as  seen  in  the  Holman  drill,  and  not  from  the  side. 
The  Seargent  air  chest  is  also  of  a  later  type  than  any  shown  in 
catalogues.  I  believe,  however,  this  valve  has  been  modified  to 
suit  these  conditions,  and  it  appears  to  be  in  many  ways  an  ideal 
device,  also  applicable  to  hammer  drills. 


VI 
PISTON  DRILLS  DESIGNED  TO  USE  AIR  EXPANSIVELY 

IT  has  been  shown,  mechanically,  that  the  piston  drill  is  a 
most  uneconomical  machine.  The  air  is  exhausted  into  the 
atmosphere  at  full  pressure,  and  where  15  to  30  h.p.  may  be  em- 
ployed at  the  steam  cylinders  of  an  air  compressor,  only  about 
1.7  h.p.  is  usefully  employed  cutting  rock.  Thus  the  cost  of 
generating  compressed  air  to  work  one  rock  drill  may  be  an  impor- 
tant item  of  cost.  On  the  Rand  it  varies  from  6s.  to  12s.  per 
10-hour  shift.  It  is  obvious  that  a  reduction  of  50  per  cent,  in 
air  consumption  would  be  an  important  saving.  It  has  already 
been  emphasized  that  this  item  is  a  comparatively  small  one  in 
the  total  daily  expenses  of  running  the  drill.  In  considering 
schemes  for  economizing  air,  the  following  questions  present 
themselves  for  answer:  Will  the  drilling  speed  be  adversely 
affected?  Will  moisture  in  the  air  on  its  expansion  choke  the 
valve  ports  with  ice,  causing  "freeze-ups"  and  stop  the  drill's 
working?  In  practice  is  the  economy  of  air  a  real  one,  or  will 
it  soon  disappear  due  to  increased  leakage,  wear,  and  tear  affecting 
the  valve  motion?  Will  extra  cost  of  supervision  and  repairs 
amount,  in  the  long  run,  to  a  sum  equal  to  the  alleged  saving  of  air? 

Let  us  take  two  cases  to  illustrate  what  different  conditions 
may  mean. 

Mine  No.  1  is  worked  by  expensive  labor.  Compressed  air 
is  generated  by  water  power,  and  is  consequently  cheap.  The 
vein  is  narrow  and  rich  in  hard  ground.  Owing  to  various  cir- 
cumstances a  large  treatment  plant  requiring  a  maximum  output 
to  supply  it  is  not  installed.  The  number  of  development  faces 
on  which  rock  drills  can  be  employed  is  limited,  and  the  present 
rock  drills  are  working  at  the  highest  economic  air  pressure. 
Will  it  pay  in  this  instance  to  install  a  rock  drill  consuming  25 
per  cent,  less  air,  but  having  a  drilling  speed  10  per  cent,  less? 
It  is  obvious  that  in  such  a  case  it  would  not  be  good  policy  to 
make  any  change,  as  what  would  be  saved  in  money  spent  in 

122 


PISTON   DRILLS  TO  USE   AIR    EXPANSIVELY  123 

generating  compressed  air  would  be  more  than  that  lost  in  other 
directions. 

At  mine  No.  2  a  compressor  is  driven  by  steam  generated  at  a 
high  cost  from  expensive  fuel.  This  plant  is  being  worked  above 
its  real  capacity,  and  the  air  pressure  has  fallen  below  the  economic 
limit.  The  prospects  of  the  mine  do  not  allow  of  further-outlay 
in  compressor  plant;  improvements  have  greatly  raised  the  capacity 
of  the  treatment  plant;  labor  is  scarce  and  numerous  faces  are 
available  for  machines;  running  costs  and  labor  are  not  high. 
The  effect  of  installing  machines  having  a  25  per  cent,  lower  air 
consumption  with  a  10  per  cent,  less  drilling  speed  would  be  that 
either  25  per  cent,  more  machines  could  be  put  to  work,  or  that 
the  air  pressure  could  be  raised  all  over  the  mine,  enabling  these 
machines  to  attain  an  equal  or  greater  drilling  speed  than  those 
formerly  employed.  With  25  per  cent,  more  machines  the  treat- 
ment plant  could  be  kept  fully  supplied  with  rock  and  costs  be 
thus  lowered. 

The  following  are  examples  of  drills  constructed  to  work 
using  air  expansively. 

Optimus  Compound  Rock  Drill.1  —  This  machine  does  not 
drill  as  rapidly  as  ordinary  machines.  Owing  to  the  long  exhaust 
ports  it  is  liable  to  freeze  up. 

The  Optimus  compound  rock  drill  is  manufactured  by  Schram, 
Harker  &  Company  of  London,  and  is  shown  in  Fig.  88.  The 
cylinder,  a,  has  a  wider  portion,  a',  and  correspondingly  the  pis- 
ton, c,  has  an  enlargement,  g.  The  air  enters  through  the  port,  6, 
into  cylinder  a,  whilst  cylinder  a'  is  in  communication  with  the 
air  ports  m  and  h.  As  the  piston  moves  forward  past  the  port  6, 
air  enters  the  valve  cylinder  r,  acts  there  on  a  larger  area  than  at 
I,  and  moves  the  valve  piston,  c,  forward,  thereby  cutting  off 
communication  with  a,  and  making  communication  between  a 
and  a'.  The  air  now  acts  on  the  larger  area  of  g,  and  thereby 
moves  the  piston  back,  past  the  port  6,  when  the  cylinder,  r,  is 
placed  in  communication  with  the  atmosphere  through  ports  b 
and  h,  and  the  valve,  /,  is  moved  back. 

The  Slugger  drill  and  the  Stephens  Climax  Imperial  drill 
have  been  already  described.  The  Imperial  drill  working  on  the 
Witwatersrand  gold  fields  cuts  off  air  at  half  stroke  forward. 

1  Drawing  and  description,  taken  from  pp.  79  and  80,  Handbook  of  Blasting, 
Oscar  Gutteman. 


124 


ROCK   DRILLS 


I 

8 
\ 


PISTON   DRILLS  TO   USE   AIR    EXPANSIVELY  125 

Konomax  Drill.  —  A  recent  and  novel  design  of  drill  is  the 
Konomax,  Fig.  89. 

The  piston  of  the  Konomax  drill  consists  of  two  portions,  AI 
and  A2,  working  in  a  corresponding  cylinder.  The  effective  area 
of  the  face  A3  being  double  that  of  the  face  A4.  The  effective 
area  of  A^  is  much  greater  than  that  of  other  piston  drills  of  similar 
diameter,  as  passages  are  made  past  the  rifle  bar,  so  that  the  air 
pressure  acts  effectively  on  the  face  A4.  This  cannot  be  done 
with  ordinary  types,  hence  this  machine  has  a  somewhat  more 
powerful  blow  for  the  same  piston  diameter.  The  air  space  of 
the  smaller  cylinder,  B',  is  in  constant  communication  with  the 
air  supply  in  the  hose  pipe  through  the  inlet  D.  The  supply  of 
air  to  the  forepart  of  the  large  cylinder  air  space  B2  is  taken  from 


FIG.  89.  —  Konomax  drill. 

Bf,  and  is  controlled  by  a  piston-spool  valve  P,  worked  by  air 
pressure  to  effect  the  following  cycles. 

The  piston  being  in  the  position  shown,  live  air  is  admitted 
from  B'  to  the  front  of  the  piston,  and  acting  on  the  face  As  (the 
area  of  which  is  double  that  of  A4)  starts  to  drive  this  piston  back 
against  the  less  pressure  on  the  face  A  4.  At  a  predetermined 
point  in  the  back  stroke,  the  valve  cuts  this  supply  off,  and  the 
air  is  allowed  to  expand.  This  point  is  generally  at  half  stroke, 
giving  an  expansion  of  1:2.  As  expansion  occurs,  the  pressure 
on  the  face  A3  is  diminished  until  it  is  only  equal  to  that  on  A±. 
This  pressure  on  A4  is  then  able  to  overcome  the  momentum  of 
the  piston  and  bring  it  to  rest.  At  this  instant  the  air  is  exhausted 
from  the  front  end  of  the  piston  by  the  movement  of  the  valve, 
and  the  piston  is  driven  forward  and  makes  a  free  stroke.  Air 
is  again  supplied  to  As  and  the  cycle  repeated. 


126  ROCK  DRILLS 

Atmospheric  pressure  is  maintained  between  the  piston  rings 
by  means  of  an  aperture  A  in  the  cylinder  walls.  This  is  in 
connection  with  the  arrangement  for  moving  the  valve.  The 
machine  thus  exhausts  air  once  in  the  cycle,  and  that  upon  the 
backward  stroke,  instead  of  twice,  as  in  the  ordinary  machine. 
The  air  is  transferred  from  B'  to  drive  the  cylinder  back. 

The  pressure  is  always  maintained  behind  the  rear  end.  This 
allows  the  valve  P  to  be  placed  right  over  the  front  end  of  the 
cylinder,  thus  making  the  exhaust  port  short  and  straight.  There 
is  thus  no  air  lost  in  clearance  spaces.  The  cold,  exhausted,  and 
expanded  air  having  a  direct  exhaust,  freezing  up  (which  would 
otherwise  occur)  is  obviated. 

Advantages  and  Disadvantages.  —  With  the  ordinary  3-in. 
piston  drill,  piston  area  7  sq.  in.,  assuming  a  stroke  of  6  in.,  the 
air  consumption  on  the  front  stroke  amounts  to  42  cu.  in.  But 
on  the  back  stroke  the  piston  area  is  diminished  by  the  area  of 
the  1-2-in.  piston-rod  and  so  is  only  5J  sq.  in.  Therefore  the  air 
consumed  on  the  back  stroke  amounts  to  31.5  cu.  in.  The  area 
of  the  valve  ports  and  clearance  is  18  X  1  X  i  in.,  or  9  cu.  in. 
Therefore  th<e  total  air  consumption  of  the  ordinary  piston  drill 
is  about  82  cu.  in.  per  double  stroke.  In  the  Konomax  drill  the 
area  of  A 3  is  14  sq.  in.,  and  the  stroke  about  6  in.  As  the  cut-off 
occurs  at  half-stroke,  the  air  consumption  of  the  Konomax  drill 
is  14  X  3  or  42  cu.  in.  Some  ordinary  piston  drills,  as  the  Climax 
and  Slugger,  can  also  be  set  to  cut  off  air  on  the  forward  stroke 
and  use  air  expansively. 

This  shows  a  theoretical  saving  of  about  50  per  cent,  air,  and 
tests  on  new  machines  are  said  to  show  this  to  be  obtained.  Owing 
to  economy  in  the  valve  chest  and  air-port  weights,  despite  the 
difference  of  size  of  cylinder,  the  weight  of  the  drill  compares 
favorably  with  the  ordinary  types. 

Its  detractors  and  competitors  question  its  power  of  rapid 
drilling  and  state  that  any  theoretical  saving  of  air  will  be  offset 
in  practice  by  increased  leakage.  Increased  leakage  is  bound  to 
occur  past  the  piston  when  worn,  as  compared  with  that  of  an 
ordinary  machine.  In  an  ordinary  machine  each  end  is  under 
pressure  half  its  time  and  the  total  leakage  surface  is  twice  C 
(where  C  equals  the  circumference  of  a  3-in.  circle,  or  9.4  in.)  for 
the  whole  working  time.  In  the  Konomax  drill  Bf  is  under  pres- 
sure for  all  of  the  working  time,  which  means  9.4-in.  leaking  sur- 


PISTON   DRILLS   TO   USE   AIR    EXPANSIVELY  127 

face,  and  also  the  6-in.  diameter  piston  ring  is  under  pressure 
half  its  time  =  9.4  in.  Therefore  the  total  leaking  surface  equals 
18.8  in.,  or  twice  that  of  an  ordinary  drill.  This  may  not,  however, 
prove  very  serious,  or  very  greatly  reduce  the  saving  of  air. 

This  system  certainly  presents  great  possibilities  in  air  econ- 
omy, both  for  piston  drills  and  for  hammer  drills.  However,  it 
has  one  great  defect  that  must  militate  against  its  use  in  certain 
work,  such  as  putting  down  long  holes  in  shafts  and  winzes.  The 
length  of  the  stroke  is  determined  by  the  gradual  equalization 
of  two  opposing  forces,  viz.,  (1)  the  air  expanding  on  the  front 
area  and  (2)  the  constant  pressure  on  the  back.  Any  addition 
to  the  latter  force  means  that  the  stroke  will  be  shortened,  and 
as  the  lifting  power  is  diminished,  the  drill  steel  will  be  inclined 
to  stick.  This  must  occur  where  the  weight  of  long  steel  is  added 
to  the  pressure  on  the  back  of  the  piston,  and  also  in  flat  dry 
holes  where  there  is  great  friction  on  the  steel.  Hence  in  such 
work  the  ordinary  type  of  machine  will  more  than  hold  its  own. 

A  trial  extending  over  a  fortnight  was  made  recently  with 
this  drill,  while  new,  against  one  of  the  standard  makes  of  rock 
drill  of  similar  sized  cylinder.  This  trial  was  carried  out  by  a 
committee  of  engineers.  Some  of  the  principal  results  were  as 
follows : 

At  65.3  Ib.  surface  air  pressure  when  drilling  the  same  average 
depth  of  hole,  63.5  in.,  and  about  the  same  percentage  of  dry 
holes,  8.5  per  cent.,  the  Konomax  used  24.4.  per  cent,  less  air 
per  inch  drilled  than  the  new  standard  machine  and  drilled  3.6 
per  cent,  faster.  Old  drills  of  the  standard  make  that  had  been 
overhauled  recently  used  59.7  per  cent,  more  air  per  inch  drilled 
than  the  new  machines.  There  are  no  figures  available  as  to 
what  the  air  consumption  of  this  type  of  machine  would  be  when 
it  was  worn,  and  what  effect  wear  of  valve  and  cylinder  would 
have  on  its  working  economy.  This  type  of  machine  has  been 
at  work  over  a  year  in  one  large  mine.  I  am  informed  that  the 
cylinders  have  not  yet  been  rebored.  General  remarks  made  in 
reference  to  this  class  of  machine,  acting  without  tappets  or 
auxiliary  valves,  must  be  considered.  Since  only  one  exhaust 
and  admission  is  required  every  stroke,  the  regulation  of  valve 
action  is  simpler  than  in  most  types.  This  cycle  of  operations, 
making  the  blow  with  live  air  all  the  way,  and  making  the  return 
by  expansion,  should  be  very  suitable  for  hammer  drills. 


128  ROCK  DRILLS 

Speaking  with  the  information  at  hand  to  date,  I  should  say 
that  the  Konomax  machine  represents  perhaps  the  most  promis- 
ing attempt  so  far  made  to  use  air  expansively  in  rock  drills;  but 
that  the  machine  cannot  yet  be  said  to  have  established  itself 
as  a  standard  type.  Earlier  models  of  this  machine  introduced 
on  the  Rand  failed,  owing  to  poor  workmanship.  Its  manufac- 
ture has  now  been  taken  up  by  a  prominent  firm  who  will  manu- 
facture it  for  certain  work,  as  well  as  their  own  model. 

The  rock  drill  is  a  heat  engine  as  much  as  a  steam  engine  is, 
and  using  air  expansively  when  it  has  not  been  reheated  has 
always  caused  trouble  where  exhaust  ports  are  of  any  length. 
Generally,  designers  of  piston  machines  have  aimed  rather  at 
getting  the  heaviest  possible  blow  for  a  given  size  of  cylinder, 
and  the  most  powerful  return  stroke  to  free  the  drill  steel  in 
difficult  holes,  rather  than  use  the  air  in  the  most  economical 
manner  possible.  In  valveless  hammer  drills,  and  in  the  Ade- 
laide and  Darlington  drill,  the  air  is  expanded  on  the  forward 
stroke.  Yet  it  is  always  claimed  that  valve-moved  machines  of 
similar  diameter  and  stroke,  using  full  air  and  full  stroke,  can 
always  bore  more  rapidly. 


VII 

THE   PHILOSOPHY    OF   THE    PROCESS    OF   DRILLING 

ROCK 

WITH  NOTES  ON  ITS  PRACTICAL  APPLICATION  IN  MODERN  TYPES 

OF  MACHINES 

To  bore  holes  in  rock  the  cohesion  of  the  rock  particles  must 
be  overcome  by  the  application  of  force.  This  may  be  done  in 
three  ways: 

(1)  By  abrasion  alone,  as  in  the  diamond  drill. 

(2)  By  combined  abrasion  and  chipping,  as  in  the  case  of 
rotary  drills  having  more  or  less  elastic  teeth.     In  this  case  the 
tension  on  the  teeth  of  the  boring  tool  may  tear  fragments  off  as 
well  as  wear  them  away.     The  Brandt  rotary  hydraulic  drill  and 
the  Calyx  core  drill  may  be  taken  as  an  example  of  this  class. 

(3)  By  percussion,  as  in  the  modern  types  of  percussive  rock 
drills.     To  bore  a  hole  by  means  of  percussion  the  drilling  tool 
must  be  as  hard  or  harder  than  the  rock.     It  must  strike  a  blow 
powerful  enough  to  chip,  disintegrate,  or  crush  the  rock. 

It  is  obvious  that  chipping  is  a  much  more  economical  and 
quicker  method  than  crushing;  but  among  the  conditions  under 
which  piston  rock  drills  are  usually  operated,  the  boring  tool 
loses  its  sharp  cutting  edge  very  rapidly.  Sufficient  force  must 
be  provided  to  enable  a  blow  to  be  struck  that  will  crush  the  rock 
under  the  blunted  edges  and  allow  progress  to  be  made. 

Two  different  systems  of  boring  rock  can  evidently  be  adopted : 
First,  a  number  of  smashing  blows  may  be  delivered  on  a  tool 
which  is  in  hard  rock,  thus  rapidly  blunting  it.  This  may  be 
called  the  method  adopted  in  designing  most  piston  drills  for 
work  in  hard  rock.  Secondly,  a  much  larger  number  of  lighter 
blows  may  be  delivered  on  a  tool  that  is  kept  sharper  during  a 
longer  period,  which  chips  rather  than  crushes. 

Again,  the  cutting  or  crushing  blow  may  be  delivered  in  two 
ways,  by  direct  or  by  indirect  impact  of  the  striking  body.  The 

129 


130  ROCK  DRILLS 

latter  method  has  been  longest  in  use  for  boring  hard  rock  by 
manual  labor.  The  cutting  edge  of  the  boring  tool  is  held  against 
the  rock  and  is  struck  by  a  separate  hammer  or  weight.  Such 
a  method  of  boring  rock  by  mechanical  means  is  employed  by 
the  modern  types  of  hammer  drills.  The  method  of  direct  im- 
pact has  been  long  employed  in  quarries  and  open  cuttings,  to 
bore  holes  by  manual  labor.  It  is  that  of  the  churn  or  jumper 
drill,  which  is  a  steel  bar,  with  its  cutting  end  sharpened  into  a 
chisel  point,  which  is  allowed  to  fall  with  its  cutting  edge  on  the 
bottom  of  a  downwardly  directed  hole.  Its  modern  represen- 
tative for  boring  by  mechanical  power  is  the  piston  type  for 
percussive  rock  drill.  In  this,  the  boring  tool  is  attached  rigidly 
to  and  forms  the  extension  of  a  piston  which  is  flung  bodily  against 
the  rock  and  withdrawn  again  by  mechanical  means. 

Theoretically,  the  best  mechanical  apparatus  for  boring  holes 
in  rock  would  be  one  that  would  consume  the  minimum  amount 
of  power  per  unit  of  rock  excavated;  one  that  would  deliver  the 
greatest  possible  number  of  blows  in  a  given  time;  one  with  a 
drill  bit  delivering  blows  in  different  radial  positions  of  the  cut- 
ting edge  around  an  axis  which  forms  a  true  extension  of  the  direc- 
tion in  which  the  force  is  applied.  In  other  words,  in  a  piston 
drill,  one  in  which  the  center  line  of  drill  bit  and  center  line  of 
cylinder  form  a  straight  line,  and  in  a  hammer  drill,  one  in  which 
a  true  blow  is  delivered  on  a  true  end  of  a  straight  drill  bit  or 
tool.  The  tool  in  both  cases  is  revolved  a  little  after  each  blow. 
Such  blows  must  be  delivered  by  a  cutting  edge  of  minimum  size 
in  relation  to  the  final  diameter  required  for  the  extreme  depth 
of  hole.  Such  blows  must  also  be  delivered  by  a  cutting  edge 
of  maximum  average  sharpness  over  its  working  period  (and  any 
changes  in  the  tools  used  must  be  made  in  minimum  time),  in 
order  that  the  rock  may  be  chipped  off  rather  than  crushed. 

Chipping  is  a  more  economical  process  of  cutting  rock  than 
crushing.  The  blows  delivered  must  be  sufficiently  heavy  to 
accomplish  the  necessary  chipping  or  crushing  action  to  bore  the 
hole,  with  the  cutting  edge  blunted  to  the  maximum  allowable 
amount;  while,  at  the  same  time,  not  so  severe  as  to  bend  or 
break  the  bit,  or  to  set  up  undue  vibration  or  stresses  in  the 
machine,  its  connections  and  supports.  The  machine  must  be 
able  to  eject  the  rock  cuttings  from  the  hole  as  soon  as  they  are 
formed,  in  order  that  none  of  the  energy  may  be  expended  in 


PHILOSOPHY  OF   PROCESS  OF   DRILLING  ROCK         131 

pulverizing  rock  already  displaced,  and  the  blow  on  the  uncut 
rock  be  thus  deadened  and  diminished  in  force. 

Construction  of  Machine.  —  The  drill  must  be  simple  in  con- 
struction, having  as  few  moving  parts,  and  as  few  parts  requir- 
ing connections,  as  possible.  These  connections  and  parts  must 
be  made  of  the  best  and  strongest  materials  to  enable  them  to 
withstand  the  incessant  and  severe  stresses  set  up  in  a  machine 
whose  very  function  is  to  produce  jar  and  concussion.  Such  a 
machine  must,  however,  also  be  of  the  minimum  weight  possible, 
in  order  that  it  may  be  handled,  transported,  set  up  ready  for 
work,  and  operated  with  as  little  labor  and  loss  of  time  as  possible. 
Such  is  the  ideal  to  be  obtained;  but  some  of  the  qualifications 
required  limit  and  oppose  one  another.  For  instance,  we  cannot 
increase  strength  when  the  best  material  is  employed  without 
increasing  weight.  For  this,  and  other  reasons,  the  rock  drill 
of  to-day,  as  a  commercial  tool,  can  only  be  a  compromise.  The 
ideal  drill  does  not  exist,  and  the  best  drill  combines  the  maxi- 
mum proportion  of  these  separate  qualifications  in  the  right  pro- 
portion of  its  relative  importance,  having  also  regard  to  the  fact, 
too  often  overlooked  by  inventors,  that  the  rock  drill  is  a  commer- 
cial tool.  That  is,  a  tool  to  economize  labor,  time,  capital,  and 
interest  charges  in  engineering  and  mining  work.  It  is  a  money- 
making,  dollar-saving  tool  to  be  operated  under  conditions  mak- 
ing the  dollar  aspect  of  the  proposition  the  predominant  one.  The 
freak  drill  is  the  product  of  the  inventor  who  does  not  understand 
this,  and  who  worries  himself  over  problems  of  percentage  of 
power  used  and  converted  into  work,  regardless,  perhaps,  of  more 
important  matters. 

Efficiency.  —  The  best  drill  is  the  most  efficient  drill.  Me- 
chanical efficiency  is  a  different  thing  from  practical  efficiency. 
The  theoretical  engineer  asks  for  a  tool  that  will  give  a  percentage 
of  efficiency  in  work  done,  approaching  that  of  the  best  triple- 
expansion  pump  in  lifting  water.  His  soul  hankers  after  electric 
transmissions.  He  is  grieved  and  indignant  that  any  one  should 
be  content  to  use  a  tool  driven  by  compressed  air,  acting  with- 
out expansion,  with  an  efficiency  of  only  a  few  per  cent,  of  the 
force  developed  at  the  prime  mover.  He  forgets  that  this  equa- 
tion holds  good  in  practice.  Let  P  =  practical  efficiency;  M  = 
mechanical  efficiency,  or  call  it  power  cost  for  running  drill; 
W  =  wages  of  operators;  C  =  cost  of  repairs  and  sharpening 


132  ROCK  DRILLS 

steel;    S  =  standing,    interest,    and    administration    charges     of 
undertaking;  F  =  feet  bored  per  unit  of  time. 
Then 

P  = 

M+w+s+c 

When. this  equation  is  reduced  to  plain  figures  in  actual  cases,  it 
is  soon  seen  that  M  forms  but  a  comparatively  small  part  of  the 
total  figure.  Such  considerations  show  that  it  would  be  folly 
to  install  any  machine  that  will  not  perform  the  most  work  for 
the  least  total  expenditure;  that  the  maximum  average  boring 
speed  over  the  total  time  of  working  is  the  most  important  fea- 
ture to  seek  for  in  a  drill;  other  things  being  equal,  the  machine 
that  will  bore  the  most  rapidly  is  the  best  machine.  Boring 
speeds  being  equal,  the  best  machine  is  the  one  that  will  cost 
least  for  maintenance  and  operation  and  consume  the  minimum 
of  power.  It  must,  however,  be  remembered  that  average  bor- 
ing speed  is  dependent  on  other  factors  than  mere  speed  of 
reciprocation,  or  weight  of  blow.  A  machine  might  excel  in 
these  respects  and  yet  break  down  so  frequently  as  to  waste  much 
time  underground  in  replacements  and  repairs.  Or,  a  drill  might 
be  so  heavy  and  unhandy  to  set  up,  that  the  proportion  of  actual 
drilling  time  to  the  actual  time  available  to  perform  work  would 
be  so  small  that  a  machine  of  slower  maximum  boring  speed, 
that  was  light  and  handy  and  could  be  kept  at  work  for  a  greater 
proportion  of  working  time,  would  be  preferable. 

In  deciding  on  the  relative  merits  of  hammer  and  piston  drills 
for  certain  work,  this  consideration  has  to  be  kept  constantly  in 
mind.  To  illustrate  the  difference  between  practical  and  mechani- 
cal efficiency,  we  may  take  an  example  from  recent  South  African 
practice.  In  general  practice  one  white  man,  with  five  natives, 
operates  two  machines.  The  cost  of  operating  for  one  shift, 
one  rock  drill  supervised  by  half  time  of  one  white  man  at  25s.  per 
day,  with  2|  natives'  time,  would  be  somewhat  as  follows.: 

s.  d. 

Cost  of  compressed  air,  6s.  6dL  to  11s.  per  shift  approx 8  6 

White  wages 12  6 

Native  wages,  food  and  compound  expenses 7  6 

Oil,  approximate —  3 

Cost  of  hose,  approximate 3 

Depreciation  and  maintenance  costs  for  the  rock  drill,  about  6  0 

Total  cost  per  shift 35          0 


PHILOSOPHY  OF   PROCESS  OF   DRILLING  ROCK         133 

This  amount  does  not  include  interest,  standing,  and  general 
charges  of  mine  or  works,  and  head  office,  if  any.  These  have  to 
be  distributed  over  the  tonnage  mined  or  feet  developed,  and  will 
be  increased  or  reduced  in  proportion  to  the  footage  bored  or 
tons  broken  per  shift.  Suppose  one  machine  drills  35  ft.  per 
shift.  Cost  per  foot  drilled  will  then  be  Is.  Another  machine 
is  constructed  to  use  only  about  half  as  much  compressed  air. 
This  may  be  done  by  using  air  expansively.  Its  cost  per  shift 
will  then  be  31s.  It  can,  however,  bore  only  28  ft.  per  shift, 
and  thus  the  cost  per  foot  bored  is  l.ls.  per  foot;  hence  it 
does  not  pay  to  work  it,  assuming  the  air  pressures  to  be  the  same, 
and  the  number  of  faces  available  for  work  to  be  limited.  In 
dealing  with  special  cases  other  factors  have  to  be  taken  into 
account,  and  these  will  be  briefly  considered  when  air  pressures 
are  discussed.  Wages  in  South  Africa  now  tend  to  lower  rates 
and  the  example  shown  is  modified. 

Conditions  under  which  Rock  Drills  Work.  —  No  other  branch 
of  mechanics  has  seen  the  invention  of  so  many  excellent,  economi- 
cal, and  apparently  mechanically  sound  devices  which,  in  prac- 
tice, have  to  be  thrown  out  as  failures.  The  reason  for  this  is 
to  be  found  in  the  conditions  under  which  rock  drills  must  work. 
A  rock  drill  constructed  to  work  in  a  nicely  swept  engine  room 
under  constant  skilled  attendance  might  possibly  be  a  very  dif- 
ferent machine  from  what  it  is.  No  portable  mechanical  appli- 
ance used  by  man  has  to  do  its  work  under  such  severe  conditions 
as  a  rock  drill  works.  It  is  usually  used  by  men  who  are  not 
mechanics,  and  who  have  no  knowledge  of  the  laws  of  force. 
They  will  often  use  full  power  and  subject  the  weakest  parts  to 
the  severest  bending  and  breaking  stresses.  Its  lubrication  is 
constantly  neglected,  and  the  oil  it  does  get  is  usually  adminis- 
tered in  large  amounts  at  rare  intervals.  The  average  miner  will 
apparently  try  his  best  to  see  which  make  of  machine  can  pass 
the  largest  proportion  of  stones  and  grit  through  its  cylinder  and 
valve  parts.  He  will  complain  if  anything  smaller  than  a  marble 
should  stop  its  working.  His  remedy  for  this  evil  will  be  to 
smash  the  top  of  the  valve  chest  in  as  a  protest  against  the  stick- 
ing of  the  valve.  His  sovereign  remedy  for  anything  irregular 
in  the  working  of  the  machine,  due  to  a  drill  bit  sticking  in  the 
hole,  is  to  take  a  hammer  and  hit  hard,  often,  and  not  to  be 
too  particular  where  he  hits.  Under  such  treatment  the  proud- 


134  ROCK   DRILLS 

est  creations  of  the  work  shop  and  office  inventor  shrivel  up  and 
disappear  from  the  realms  of  realities.  The  modern  type  of 
rock  drill  may  be  considered  as  one  of  the  most  wonderful  products 
of  inventive  genius,  when  one  realizes  the  manner  in  which  the 
best  possible  qualities  have  been  preserved  and  the  manner  in 
which  difficulties  have  been  overcome.  To  do  this,  however,  has 
called  for  the  best  work  that  civilization  can  supply  in  selected 
materials  and  high-grade  workmanship.  The  rock  drill  has  by 
no  means  reached  perfection  and  the  lines  of  possible  improve- 
ment are  indicated  as  the  defects  and  merits  of  the  three  classes 
of  machine  are  considered,  and  are  compared  with  the  ideal 
drill. 

Rotary  Pressure  Drills  vs.  Percussion  Drills.  —  We  are  not  here 
concerned  with  diamond  drills.  The  Brandt  drill  has  been  used 
in  tunnel  work,  the  power  being  supplied  by  hydraulic  pressure 
at  900  to  1400  Ib.  per  square  inch.  It  might  be  asked,  could  not 
some  such  machine  be  employed  in  deep  mines  where  natural 
heads  of  water  could  be  obtained,  as  by  this  system  boring  pro- 
ceeded at  as  great  a  rate  as  with  percussive  drills  ?  Here  certainly 
the  force  is  applied  economically,  the  jar  of  percussion  is  eliminated, 
water  is  easily  passed  down  a  hollow  boring  tool,  removing  broken 
rock  at  once,  and  thus  fulfilling  one  of  the  ideal  conditions 
desirable.  Practical  difficulties  arise,  however.  The  water  used 
must  be  freed  from  grit  and  contain  no  acid.  The  machine  must 
be  very  heavy  and  mounted  in  a  most  rigid  manner  to  withstand 
the  enormous  pressure  necessary  to  be  applied  to  the  teeth  of  the 
boring  tool ;  hence  it  cannot  be  made,  portable  to  secure  easy  and 
rapid  change  to  occupy  a  new  position.  The  pipe  installation  in 
a  mine  necessary  to  carry  such  enormous  water  pressures  would 
be  too  costly  to  install  and  maintain.  In  actual  work  in  the 
hardest  rock  the  efficiency  falls  off  greatly.  There  are  so  many 
moving  parts  and  connections  that  time  lost  in  repairs  or  install- 
ing spare  machines  is  a  serious  item.  Rotation  might  be  ob- 
tained in  a  lighter  and  simpler  machine  by  the  employment  of  a 
turbine  or  water  wheel  system,  but  most  of  the  difficulties  men- 
tioned would  remain.  Electric  rotary  drills  have  proved  capable 
of  boring  in  soft  rock;  but  it  is  scarcely  to  be  expected,  despite 
the  opinion  of  eminent  authorities  like  Professor  Louis,  that  they 
will  be  able  to  compete  with  percussive  drills  for  boring  really 
hard  rock.  The  chief  reason  is  not  hard  to  find.  To  overcome 


PHILOSOPHY  OF  PROCESS  OF  DRILLING  ROCK         135 

the  cohesion  of  the  particles  of  hard  rock  requires  the  application 
of  an  enormous  force.  Percussive  tools  are  expressly  designed 
to  store  up  force  as  kinetic  energy  in  moving  the  striking  tool 
and  to  deliver  it  in  its  most  effective  way,  suddenly,  on  a  cleaving, 
wedge-shaped  cutter.  Now  rotary  movement  cannot  do  this 
effectively.  Some  storing  up  of  energy  can  be  performed  in 
inducing  torque  in  the  stem  of  the  boring  tool  or  teeth  of  the  cut- 
ting tool;  but  not  nearly  as  much  as  by  storing  energy  in  a  moving 
body.  Then,  to  bore  hard  rock  effectively,  by  rotary  tools,  we 
must  have  very  great  pressure  exerted,  and  this  would  require 
heavy,  cumbersome  fittings  and  mountings,  and  an  enormous 
turning  force.  Electricity  can  give  this  only  by  means  of  gearing. 
Gearing  is  almost  out  of  the  question  in  a  mine  tool  such  as  the 
rock  drill.  Small  or  moderate  pressures  and  any  speed  of  rota- 
tion within  practical  limits  cannot  bore  hard  rock  as  rapidly  as 
pneumatic  percussion  tools.  The  diamond  drill  should  show  the 
impossibility  of  manufacturing  a  practical  electrical  rotary  drill 
for  hard  rock  work.  Professor  Henry  Louis,  however,  is  of 
another  opinion.  He  says: 

"My  own  impression  is  that  the  ultimate  solution  of  the  drill- 
ing problem  will  be  found  in  the  adoption  of  an  electrically  driven 
rotating  drill.  The  advantages  of  such  a  drill  in  rock  soft  enough 
to  admit  of  its  use  under  present  conditions  are  sufficiently  obvi- 
ous. For  example,  electrically  driven  twist  drills  are  doing 
excellent  work  in  the  comparatively  soft  ore  of  the  Cleveland 
ironstone  mines,  and  I  have  already  mentioned  how  completely 
the  rotating  hand  machine  of  the  coal  miner  has  displaced  the 
percussion  jumper.  The  success  of  the  hydraulically  driven  ro- 
tary Brandt  drill  in  the,  Simplon  tunnel  will  be  fresh  in  the  mem- 
ories of  many  here;  the  same  drill  has  also  done  good  work  in 
several  mines  where  the  workings  are  large  enough  to  enable  a 
3-in.  bore  hole  to  be  used  with  advantage.  This  drill  works  under 
heavy  hydraulic  pressure  (700  Ib.  to  2000  Ib  per  square  inch), 
but  its  rate  of  rotation  is  slow,  being  only  three  to  ten  revolutions 
per  minute. 

"An  electrically  driven  drill  will  necessarily  have  to  rotate 
at  a  relatively  high  speed,  and  it  seems  safe  to  predict  that  such 
machines  will  come  into  use  as  soon  as  a  suitable  material  for  the 
cutting  edge  of  the  drill  shall  be  discovered;  here  again  we  need 
a  metal  distinctly  harder  than  quartz  at  least,  and  strong  enough 


136  ROCK  DRILLS 

to  resist  the  severe  torsional  strains  to  which  it  will  be  exposed. 
I  am  a  very  strong  advocate  of  rotary  drilling,  not  only  because 
I  consider  it  as  mechanically  the  better  system,  but  because  I 
hold  that  it  will  afford  the  most  complete  solution  of  the  dust 
problem.  It  is  now  fairly  well  established  that  that  dread  disease, 
miner's  phthisis  (or  "  silicosis ") ,  the  greatest  danger  to  health  to 
which  the  miner  is  exposed,  is  largely  due  to  the  inhalation  of  the 
fine  sharp-edged  particles  of  mineral  thrown  off  by  the  action 
of  the  percussive  drill.  Something  has  been  done  to  combat 
this  danger  of  late  years,  notably  by  the  use  of  jets  or  sprays  of 
water,  and  particularly  by  the  use  of  hollow  drill  steels,  through 
which  a  stream  of  water  can  be  carried  to  the  very  face  of  the 
drill  hole,  but  I  am  inclined  to  think  that  it  is  only  by  rotary 
boring,  of  course  with  the  aid  of  water,  that  this  deadly  enemy 
can  be  overcome." 

Hammer  vs.  Piston  Drills.  —  Let  us  now  inquire  how  nearly 
a  practical  machine,  built  on  the  lines  of  a  piston  drill  to  bore 
rock  by  the  means  of  direct  impact,  can  be  made,  or  is  made,  to 
approach  our  ideal  machine.  What  are  its  advantages  and  dis- 
advantages as  compared  with  hammer  drills  or  those  boring  rock 
by  indirect  impact?  H.  P.  Gillette  is  the  only  writer  I  know  of 
who  appears  to  have  any  clear  ideas  on  the  relative  efficiencies 
of  so-called  " churn"  drilling  against  hammer  drilling.  He  neg- 
lects several  practical  considerations  that  must  be  accounted 
for  in  actual  work.  He  notes  that  in  hammer  drilling  a  large 
proportion  of  the  energy  of  the  blow  is  consumed  in  compressing 
the  head  of  the  drill,  the  shank,  and  the  hammer  itself.  He 
states  that  in  driving  piles  in  soft  mud  65  per  cent,  of  the  energy 
is  lost  in  heating  the  pile  head.  The  longer  the  pile  the  greater 
the  loss.  He  says  this  loss  does  not  occur  in  churn  drilling  and 
thinks  the  element  of  time  involved  in  chipping  off  the  rock 
an  important  factor,  for  when  the  bit  strikes  the  rock  a  wave  of 
compression  travels  up  several  feet  before  the  energy  of  the  mov- 
ing tool  is  all  imparted  to  the  rock,  producing  a  gradual  and  steady 
wedging  action.  This,  he  says,  should  be  theoretically  more 
effective  than  the  sudden  action  of  a  hammer  drill,  and  in  prac- 
tice it  is.  In  the  comparison  of  actual  makes  of  piston  and  ham- 
mer drills  these  conclusions  must,  I  think,  be  modified. 

The  makers  of  the  Leyner  drill  claim  that  it  will  bore  faster 
than  any  piston  drill  of  equal  diameter;  that  it  is  lighter;  that 


PHILOSOPHY  OF   PROCESS  OF   DRILLING   ROCK         137 

less  time  is  spent  in  erecting  and  moving;  that  less  time  is  lost 
in  changing  steel;  that  it  does  not  stick  in  holes,  and  that  it 
has  less  parts  than  a  piston  drill.  They  also  claim  that  it  is  an 
established  fact  in  mechanics  that  "  every  particle  of  energy  im- 
parted to  the  drill  steel  is  used  in  useful  work";  that  none  of  the 
energy  of  the  blow  is  employed  in  grinding  or  chipping  up  rock 
already  loosened,  thus  deadening  the  blow;  that  the  drill  bit 
retains  its  cutting  edge  longer  because  it  is  cooled  by  the  water 
passing  down  its  hollow  center,  and  that  it  does  not  lose  its  gage 
so  readily.  I  think  it  is  proven  that  for  holes  of  moderate  depth 
the  hammer  drill  utilizes  a  larger  proportion  of  the  energy  stored 
in  the  operating  fluid  than  does  the  standard  type  of  rock  drill, 
though  in  view  of  the  results  given  by  piston  drills  in  the  recent 
stope  drill  tests  in  South  Africa  this  statement  may  require  to 
be  modified  as  regards  down-holes.  It  is  true  that  as  the  length 
of  steel  increases  the  efficiency  rapidly  falls  off.  The  stored  en- 
ergy in  the  moving  hammer  has  first,  if  a  striking  pin  is  employed, 
to  overcome  its  inertia,  compress  it,  and  if  it  is  not  in  very  close 
contact  with  the  drill  bit  it  must  be  moved.  This  absorbs  en- 
ergy. The  rebound  of  the  drill  has  to  be  overcome,  the  drill  moved 
forward  and  compressed.  As  no  force  is  required  to  reverse  the 
weight  of  chuck  and  drill  steel  when  pulling  them  forcibly  out  of 
a  hole,  where  they  are  inclined  to  stick,  as  in  a  piston  drill,  air 
could  be  employed  expansively  more  easily  in  hammer  drills. 
As  the  cuttings  are  ejected  by  water  or  air  passed  down  hollow 
steel,  it  is  not  necessary  to  depend  on  any  churning  or  a  splashing 
action,  which  calls  for  a  long  stroke  on  piston  drills;  hence  a  short 
stroke  of  the  hammer  can  be  employed,  and  the  blows  struck  per 
minute  made  more  numerous,  which  in  mechanics  means  that 
more  work  can  be  done  with  a  lighter  machine  in  a  given  time. 

The  compressed  air,  in  most  modern  types  of  piston  drills,  is 
not  used  expansively  and  there  is  a  large  loss  of  air  in  provid- 
ing clearance  spaces  at  one  end  of  cylinder  and  in  valve  parts. 
We  are,  however,  considering  the  amount  of  energy  stored  in  the 
moving  piston  and  drill  that  is  turned  into  useful  work  in  rock 
cutting.  This  force  is  reduced,  first  by  friction  in  the  cylinder 
due  to  piston  rings,  tappets,  auxiliary  valves,  and  loose  fit  due 
to  wear.  Since  in  a  piston  drill  severe  side  stresses,  not  fully 
taken  up  by  front-head  bushing,  are  often  thrown  on  the  boring 
tool;  side  friction,  due  to  this  cause,  is  greater  than  in  hammer 


138  ROCK   DRILLS 

drills.  In  hammer  drills  no  side  stresses  come  on  the  piston 
hammer,  which  has  no  piston  rings,  tappets,  etc.,  to  reduce  its 
velocity,  but  is  generally  ground  in  to  fit  cylinder. 

The  next  cause  of  loss  of  energy  is  through  the  drilling  tool 
not  striking  blows  in  a  radial  direction  around  a  true  center  coin- 
ciding with  the  axis  of  the  piston  and  cylinder.  In  the  hammer 
drill,  the  cutting  edge  is  always  on  or  very  near  the  bottom  of 
the  hole,  while  in  standard  piston  drills  it  is  withdrawn  about 
6  in.  at  every  return  stroke  made.  Since  the  drill  mounting 
cannot  be  made  quite  rigid  its  vibration  always  tends  to  throw 
the  drill  bit  against  the  side  of  the  hole.  In  actual  work  also  quite 
an  appalling  loss  of  energy  is  caused  by  bent  steel  and  steel  sharp- 
ened so  that  the  wings  of  the  cutting  edge  are  of  unequal  length, 
and  by  neglect  to  keep  chuck  bushings  in  repair.  Later  experi- 
ences have  shown  that  instead  of  there  being  no  loss  of  energy 
in  the  drill  steel  of  a  standard  piston  drill,  this  loss  is  very  great 
owing  to  lack  of  rigidity.  It  has  been  found  that  thickening  the 
shank  and  stem  of  drills  used,  increases  the  efficiency  very  greatly. 
The  gradual  wedging  action  of  their  blow  (if  it  exists)  is  not,  I 
think,  of  any  advantage  in  practice,  as  bits,  are  so  soon  dulled 
that  the  bit  mostly  crushes  the  rock  rather  than  chips  it.  Loss 
again  occurs  in  drilling;  the  force  of  the  blow  is  reduced  by  pieces 
of  cut  rock  interposing  themselves  before  the  edge  of  the  bit  at 
the  bottom  of  the  hole,  and  in  the  form  of  mud  or  dust  impeding 
the  movement  of  the  drill.  These  losses  are  most  serious  in  drill- 
ing up  holes  slightly  inclined  above  the  horizontal,  as  in  a  drift 
or  a  vein  or  small  tunnel. 

Hammer  Drill.  —  Did  one  not  remember  the  axiom,  that 
the  rock  drill  is  a  commercial  machine,  one  might  be  tempted  to 
believe  that  in  all  cases  the  modern  hammer  drill  is  by  far  the 
superior  machine.  We  may  now  ask:  What  are  the  defects  of 
hammer  drills  and  the  drawbacks  to  their  use?  In  dealing  with 
a  subject  like  this  one  must  remember  that  improvements  in 
design  and  manufacture  are  constantly  being  made.  For  in- 
stance, I  have  a  good  deal  of  information  regarding  the  perform- 
ance of  model  V,  Leyner  machine,  in  South  Africa  and  Australia; 
but  as  far  as  I  am  aware  model  VI,  of  which  it  is  claimed  that 
most  of  former  defects  have  been  removed,  has  not  been  tried 
outside  America.  The  kinetic  energy  of  a  blow  is  the  product 
of  one-half  the  mass  of  the  moving  body  multiplied  by  the  square 


PHILOSOPHY  OF  PROCESS  OF  DRILLING  ROCK         139 

of  the  velocity.  In  other  words,  to  double  the  energy  of  a  blow 
it  would  be  necessary  to  double  the  mass,  or  weight,  if  the 
velocity  is  the  same;  but  to*  double  the  energy  keeping  the  mass 
the  same  the  velocity  must  be  increased  four  times.  The  weight 
of  the  piston  hammer  of  the -largest  type  of  hammer  drill  is  15  Ib. 
The  weight  of  piston,  steel,  etc.,  of  a  piston  drill  varies  from  60 
to  125  Ib.,  so  that  a  blow  of  equal  force  can  be  delivered  by  a 
hammer  drill  only  by  increasing  the  velocity  of  the  hammer  very 
greatly.  This  is  acknowledged,  for  as  one  hammer-drill  maker 
states,  the  weight  of  the  piston  is  one-fourth  that  of  a  piston  drill; 
but  the  velocity  is  four  times  as  great.  To  give  a  blow  equal  in 
power  it  should  be  sixteen  times  as  great!  The  length  of  stroke 
is  also  only  half  that  of  a  piston  drill,  and  of  course  the -number 
of  blows  per  minute  is  greatly  increased.  Now,  if  the  losses  of 
energy,  in  heating  the  hammer  and  drill,  in  creating  vibrations, 
in  overcoming  the  inertia  of  the  drill  and  striking  pin,  approach 
65  per  cent,  as  in  pile  driving,  when  using  a  long  steel  a  very 
heavy  blow  must  be  struck  to  get  velocity  enough  on  the  hammer. 
This  means  using  very  high  air  pressures  up  to  100  Ib.  Where, 
owing  to  circumstances,  such  high  pressures  cannot  be  carried, 
the  drill  will  not  strike  a  heavy  enough  blow  to  compete  at  all 
with  piston  drills.  It  must  also  be  remembered  that  a  tremen- 
dous force  has  been  freed  inside  the  drill  itself,  and  that,  if  by  acci- 
dent it  is  not  expended  on  the  end  of  the  drill,  it  will  tend  to  cause 
breakage  of  front  heads,  anvil  blocks,  and  cylinders  unless  the 
device  of  side  rods  and  springs  is  not  adapted  from  the  piston 
drill,  or  other  buffers  put  in.  This  of  course  holds  true  also  with 
piston  drills.  With  such  rapidly  moving  parts,  in  the  presence 
of  grit,  wear  is  very  rapid;  but  the  greatest  trouble  is  due  to  the 
effect  of  the  vibrations  set  up  by  the  blows  struck.  This  crystal- 
lizes and  breaks,  first,  the  cutting  edges  of  the  bit,  unless  they 
are  most  carefully  designed  and  tempered.  The  steel  itself, 
especially  at  the  welds,  if  any,  is  a  source  of  constant  weakness. 
The  heads  have  to  be  hardened  or  they  crush,  and  if  hardened, 
frequently  break.  The  anvil  blocks,  the  front  head,  chuck,  and 
cylinder,  of  machine  all  suffer.  The  piston  hammer  itself,  espe- 
cially in  the  valveless  types,  where  it  is  weakened  by  having 
passages  cut  in  it,  tends  to  burst  and  may  thus  injure  the  cylin- 
der. In  one  type  of  small  drill  which  sought  to  economize  weight 
by  using  a  light  hammer  with  a  very  long  stroke,  the  kinetic 


140  ROCK  DRILLS 

energy  of  the  blow  was  so  great  that  the  stresses  set  up  per 
square  inch  of  striking  surface  were  greater  than  the  steel  com- 
prising the  anvil  block  could  possibly  stand. 

Again,  bitter  experience  has  shown  that  trouble  is  encountered 
at  once  when  water  is  introduced  into  a  drill  to  be  used  with  hol- 
low steel  for  washing  out  holes.  In  mines  it  is  not  easy  to  regu- 
late pressures  to  be  neither  too  great  nor  too  small.  Hose,  cocks, 
fittings,  and  tanks  cause  great  trouble  and  expense.  The  water 
supply,  owing  to  sediment  or  chips  present,  often  gets  choked  j  ust 
when  wanted;  but  the  worst  trouble  is  due  to  the  acidity  so  fre- 
quently found  in  mine  waters.  This,  owing  to  the  conditions  of 
Avork  where  the  machine  lies  idle  between  working  periods,  has  a 
destructive  effect  that  cannot  be  guessed  until  seen.  No  matter 
how  effective  may  be  the  means  employed  to  prevent  water 
entering  the  cylinder  of  a  machine,  wear  takes  place  in  actual 
work,  and  water  enters  and  hinders  valve  action;  after  a  time  it 
corrodes  every  part  of  the  cylinder  with  which  it  comes  in  contact. 

In  soft  rock,  the  vibrations  set  up  are  not  so  violent  and  the 
wear  and  tear  on  hammer  drills  is  less,  while  their  water  or  air 
service  makes  them  very  rapid  borers,  especially  in  flat  or  up- 
holes,  as  compared  with  piston  drills.  In  heavy  ground  the  piston 
drill  is  liable  to  stick,  owing  to  the  blow  glancing  off  some  hard 
face.  The  merits  and  limitations  of  the  smaller  types  of  hammer 
drills  are  dealt  with  in  the  chapter  on  hammer  drills.  The  turn- 
ing of  the  drill  is  more  difficult  to  manage,  mechanically  and 
automatically,  in  hammer  drills,  as  the  point  of  the  tool  is  kept 
pressed  up  to  the  rock  face  all  the  time,  making  the  friction  much 
greater. 

In  dealing  with  the  future  developments  of  the  rock  drill,  and 
in  the  description  of  several  modern  machines,  I  have  endeavored 
to  show  how  these  numerous  losses  of  energy  in  both  types  may 
be,  perhaps,  reduced,  and  in  the  description  of  several  modern 
hammer  drills  it  will  be  seen  how  the  various  difficulties  I  have 
indicated  are  minimized  or  overcome  by  improved  design  and 
material. 


VIII 
REPAIR   AND    MAINTENANCE   OF   ROCK   DRILLS 

OWING  to  the  service  it  has  to  perform  and  to  the  conditions 
under  which  it  must  work,  the  rock  drill  is  subjected  to  great 
wear.  This  wear  tends  directly  in  all  cases  to  decrease  its  effi- 
ciency and  to  increase  its  operating  cost.  In  many  mining  fields 
this  seems  to  be  forgotten,  and  some  managers  pride  themselves 
on  the  low  cost  per  month  for  repairs  and  renewals. 

Repairs  Made  by  Contract.  —  At  some  mines  the  practice  of 
letting  the  machines  out  on  contract  to  a  rock-drill  fitter  at  so 
much  a  month  per  machine  is  carried  on.  A  more  vicious  arrange- 
ment it  is  impossible  to  conceive,  as  it  is  then  to  the  fitter's  interest 
to  neglect  repairs,  and  to  refuse  spare  parts  to  the  miners  for 
renewals.  At  other  mines,  however,  the  firm  supplying  the  rock 
drills  contract  to  keep  them  in  repair  for  a  fixed  sum  per  month. 
The  company  appoints  an  official  to  make  a  monthly  inspection 
of  all  machines,  and  is  entitled  to  call  for  any  needed  repairs  to 
be  done  at  once.  This  system  is,  I  believe,  employed  in  the 
mines  under  the  supervision  of  E.  J.  Way  on  the  Witwatersrand 
gold  fields. 

MAINTENANCE  OF  PISTON  DRILLS 

I  take  the  following  clauses  from  a  specification  drawn  by 
W.  C.  Docherty  and  published  in  the  Journal  of  the  Mechanical 
Engineers'  Association  of  the  Transvaal,  with  notes  and  com- 
ments of  my  own. 

Cylinders.  —  Cylinders  of  all  machines  are  to  be  kept  in  such 
repair  that  no  undue  slackness  shall  exist  between  them  and  the 
cradle  bearings  or  guides.  They  must  be  equally  firm  at  all 
points  and  in  any  position.  The  difference  in  diameter  between 
the  bore  of  the  cylinder  and  the  diameter  of  the  piston  must 
never  exceed  ^  in.  When  this  limit  is  reached  the  cylinder  must 
be  bored  out  and  provided  with  a  new  piston.  The  piston  must 
be  ground  into  the  cylinder  and  made  the  tightest  working  fit 

141 


142  ROCK  DRILLS 

possible.  All  joint  faces  must  be  kept  straight  and  true  to  pro- 
vide good  air-tight  joints. 

Notes :  When  wear  on  the  cradle  guides  (it  is  greatly  increased 
by  the  vibration  of  the  machine)  becomes  excessive,  due  to  grit 
which  enters  between  the  surfaces,  especially  in  drilling  up-holes, 
the  cylinder  is  not  held  firmly  enough  to  strike  a  blow  with  the 
drill  bit  twice  in  the  same  place.  This  is  most  noticeable  when 
the  machine  is  run  out  to  its  greatest  extent  on  the  feed-screw. 
Wear  takes  place  most  at  the  front  portion  of  the  guides  and 
cannot  be  taken  up  quite  satisfactorily  by  means  of  inserting 
parallel  strips.  All  the  standard  makes  have  arrangements  for 
taking  up  this  wear.  In  the  Ingersoll  machines  wear  on  hori- 
zontal faces  is  taken  up  by  planing  down  the  guide  pieces  or  the 
cradle.  Wear  on  vertical  faces  is  taken  up  by  inserting  strips  of 
plate  and  turning  them  over  at  the  ends  so  that  they  cannot 
come  out.  If  these  strips  can  be  procured  with  thicker  metal 
towards  the  front,  the  uneven  wear  is  better  taken  up.  In  the 
Slugger  and  Rand  types  of  machines,  strips  of  lead  or  other  metal 
can  be  taken  from  between  the  cradle  and  the  top  pieces  of  the 
guides,  which,  as  in  the  Ingersoll  machines,  are  bolted  on  it. 
Both  these  types  occasionally  give  trouble,  owing  to  the  vibration 
loosening  the  nuts.  Often  these  have  to  be  burred  on.  It  will 
pay  in  every  case,  I  think,  to  use  helicoid  lock  nuts  instead  of 
the  usual  plain  nut,  which  is  on  the  guides  in  nearly  all  machines. 
In  the  Holman  machines,  set  screws  press  and  hold  down  wear- 
ing strips  as  required  to  allow  for  wear.  In  the  " Climax"  drill 
both  cylinder  and  cradle  are  reversible,  end  for  end,  and  the 
guides  are  also  adjustable  by  a  simple  wedge  device. 

In  several  other  makes  the  cradles  are  made  from  malleable 
cast  iron,  and  wear  can  be  taken  up  by  hammering  the  guides  in 
or  down.  The  stipulation  that  wear  between  cylinder  and  piston 
should  not  exceed  -fa  in.  is  rather  a  course  of  perfection,  I  am 
afraid.  The  practice  of  different  makers  varies.  The  Ingersoll 
company  make  their  pistons  very  hard,  and  they  do  not  wear  as 
much  as  the  cylinder.  They  supply  pistons  increasing  by  TV  in. 
in  diameter,  and  when  the  wear  becomes  excessive  with  the  clear- 
ance between  cylinder  and  piston  too  great,  the  cylinder  is  bored 
out  at  the  mine  to  fit  a  piston  yV  in.  larger.  With  a  3J-in.  machine 
pistons  are  sold  3J  in.,  3tV  in.,  and  3f  in.  When  the  last  has  been 
used  the  cylinder  must  be  thrown  away.  Holman  &  Company 


MAINTENANCE  OF  ROCK   DRILLS  143 

supply  rough  pistons  somewhat  softer  which  can  be  turned  up 
at  the  mine  to  fit  the  worn  cylinder,  which  is  first  bored  out 
true.  For  some  reason,  not  clear,  makers  have  not  adopted  the 
principle  of  using  renewable  bushings  or  liners  for  their  cylin- 
ders. These  could  be  made  and  sold  cheaply  and  could  also  be 
made  with  small  differences  of  diameter,  so  constructed  that  they 
could  be  easily  changed  and  would  work  without  leakage.  Piston 
rings  certainly  reduce  leakage  even  when  the  cylinder  is  worn; 
yet,  once  the  piston  becomes  slack  in  the  cylinder,  extra  wear 
and  stresses  are  thrown  on  to  the  liners  of  the  front  head. 
Monthly  inspections  of  all  machines  in  a  mine  always  pay.  The 
reader  is  referred  to  the  chapter  on  Rock  Drill  Tests  giving  dif- 
ference in  performances  of  old  machines  in  good  and  bad  repair 
in  the  Meyer  &  Charlton  mine,  Johannesburg. 

Slide  Valves  and  Valve  Chests.  —  Slide  valves  and  their  seat- 
ings  shall  be  periodically  repaired  and  made  perfectly  straight, 
scraped  up  to  a  surface  plate  and  adjusted  to  the  best  working 
conditions,  the  chests  also  being  kept  air-tight  to  insure  the  best 
possible  conditions  for  obtaining  the  maximum  efficiency  from 
the  machines. 

Piston  Valves  and  Valve  Chests.  —  These  are  to  be  kept  in 
perfect  order.  The  difference  in  diameter  between  valve  and 
bore  of  chest  must  not  exceed  T£iy  in.  When  this  limit  is  reached 
the  chest  must  be  reamed  out  perfectly  parallel  and  a  new  valve 
fitted  and  ground  in  to  the  neatest  possible  working  fit.  All 
joint  faces  must  be  kept  straight  and  ground  true,  to  provide  good 
air-tight  joints. 

Note:  Most  makers  sell  two  sizes  of  spindle  valves,  larger  by 
TV  in.,  for  turning  down  to  fit  rebored  air  chests.  The  proper 
fit  for  a  spindle  or  piston  valve  in  an  Ingersoll  air  chest  is  such 
that  when  the  air  chest  is  held  in  the  hand  and  reversed  the  valve 
slides  slowly  over  by  its  own  weight,  i.e.,  it  does  not  fall  quickly 
or  stick.  Undue  wear  is  indicated  by  the  piston  striking  the 
back  end  of  cylinder. 

Throttle  Valves.  —  All  throttle  valves  are  to  be  regularly  over- 
hauled, reground,  and  the  handles  are  to  be  kept  in  good  order. 
Leakage  in  throttle  valves  is  one,  I  believe,  of  the  main  causes 
of  leakage  loss  and  lack  of  efficiency  in  machines.  This  must  be 
watched  very  carefully,  and  the  fitter  not  allowed  to  send  machines 
below  unless  these  valves  are  in  order. 


144  ROCK  DRILLS 

Rockers,  Tappets,  and  Auxiliary  Valves.  —  These  must  be 
examined  for  wear  carefully  and  regularly,  and  repaired  or  replaced; 
care  being  taken  that  they  are  of  the  exact  form  and  size  for  mov- 
ing the  valve  at  the  right  point  of  the  piston  stroke.  In  the 
Ingersoll  machines  the  wear  on  the  auxiliary  valve  can  be  allowed 
for  by  taking  out  a  liner  or  liners  between  the  valve  chest  and 
cylinder.  This  lowers  the  valve  into  the  cylinder  and  makes  up 
for  its  shortening  due  to  wear,  which  retards  the  reversal  of  the 
valve.  Wear  on  tappets  generally  has  the  effect  of  shortening 
the  stroke  and  causing  greater  cushioning  of  blow.  The  bearings 
for  the  rocker  in  such  a  machine  as  the  Giant  drill  must  also  be 
inspected,  as  too  great  play  makes  the  valve  movement  short. 

Rotating  Gear.  —  This  must  be  inspected  and  kept  in  such 
repair  that  a  minimum  of  side  lash  between  the  teeth  of  the  rifle 
bar  and  nut  is  secured.  The  limit  of  play  must  not  exceed  iV  in. ; 
this  being  reached,  a  new  tight-fitting  rifle  nut  must  be  put  in. 
These  nuts  are  generally  of  brass.  Ratchet  wheels  and  pawls 
must  be  inspected  for  wear,  and  especially  the  springs,  so  that 
rotation  will  always  be  perfect. 

Front  Heads.  —  These  are  to  be  kept  in  perfect  alignment  and 
properly  packed;  the  limit  of  wear  between  the  diameter  of  its 
bore  and  piston-rod  to  be  -5?  in. ;  if  this  is  exceeded  the  front  head 
must  be  renewed  or  rebushed.  They  require  renewal  at  least 
every  month  or  oftener. 

Back  Heads.  —  These  should  be  renewed  if  cracked,  and  pro- 
vided with  all  necessary  buffers  or  springs. 

Piston  and  Piston-Rods.  —  All  pistons  are  to  be  provided  with 
suitable,  well-fitting  piston  rings  and  springs  to  prevent  any 
leakage  of  air.  The  pistons  when  being  fitted  to  a  cylinder  are 
to  be  ground  into  place  and  to  be  made  the  tightest  possible  work- 
ing fit;  the  wearing  faces  to  be  case-hardened.  The  limit  of  wear 
is  to  be  iV  in.  That  portion  of  the  piston,  or  chuck  rod,  which 
slides  through  the  front  head  is  to  be  maintained  in  good  condi- 
tion, parallel  and  smooth,  without  grooves  or  dents,  due  too  often 
to  being  struck  with  hammer,  that  may  tend  to  wear  the  packing. 
My  remarks  with  regard  to  cylinders  apply  here. 

Chucks.  —  These  are  to  be  kept  in  good  order,  the  bushings 
to  be  a  good,  tight,  driving-fit  into  the  hole  in  the  chuck.  The 
limit  of  wear  in  bushings  is  to  be  ^V  in.,  when  they  must  be  with- 
drawn and  renewed.  In  withdrawings,  the  chuck  must  not  be 


MAINTENANCE  OF  ROCK  DRILLS  145 

heated,  but  the  bushing  cut  out.  The  chuck  keys  are  to  be  kept 
in  order  with  seat  for  chuck  bolt  and  drill  shank.  The  bore  of 
bushings  must  be  perfectly  circular  and  perfectly  central.  Neglect 
of  chuck  is,  I  believe,  the  greatest  cause  of  inefficiency  in  mining 
work.  A  manager  who  takes  the  trouble  to  try  his  machines  when 
at  work  down  below,  for  eccentricity,  by  putting  in  a  starter  drill 
and  revolving  the  chuck  slowly,  having  the  bit  near  a  fixed  point  so 
that  its  distance  from  it  every  quarter  turn  can  be  noted,  will 
often  be  surprised  even  when  he  believes  his  machines  are  well 
looked  after.  It  must  not  be  forgotten  that  two  causes  tend  to 
produce  eccentricity,  or,  in  other  words,  make  the  drill,  when 
starting  a  hole,  strike  each  time  in  a  different  place.  When  the 
hole  is  at  last  started  with  a  bent  bit,  enormous  friction  and  side 
wear  is  caused  on  the  drill  bit  every  time  a  blow  is  struck,  thus 
wasting  energy  and  reducing  by  a  large  percentage  the  speed  of 
boring.  For  instance,  if  the  shank  of  a  5-ft.  bit  is  iV  inch  out 
of  line  in  the  chuck  it  throws  the  center  of  bit  out  i  inch 
and  bit  tends  to  describe  a  circle  of  1J  inches.  This  also 
throws  side  stresses  on  the  machine  and  drill,  tending  to  bend 
or  break  both.  The  first  cause  is  the  neglect  to  renew  bush- 
ings frequently.  The  second,  which  is  generally  quite  over- 
looked, is  due  to  the  fact  that  the  shanks  of  the  drills 
themselves  wear.  Drills  require  reshanking  as  soon  as  they 
are  not  a  neat  fit  in  a  new  bush.  How  often  this  occurs  de- 
pends on  circumstances;  but  the  blacksmith  should  be  made  to 
try  all  drill  shanks  on  a  new  bush  every  month  and  reshank 
any  drills  requiring  it.  Neglect  to  renew  either  causes  worse 
wear  on  the  other.  When  using  80-lb.  air  I  renew  chuck  bush- 
ings every  month  or  oftener.  In  renewing  chuck  bushings 
many  think  that  it  takes  too  long  to  cut  the  bushings  out 
and  the  chuck  is  heated.  This  after  some  time  tends  to  frac- 
ture it  between  the  holes  for  the  U-bolt,  and  the  whole  pis- 
ton must  be  thrown  aside.  If  the  chuck  bushing  is  split  where 
it  is  cut  out  for  the  pad,  and  then  crushed  in,  it  comes  out 
easily.  In  the  numerous  half-bushing  patent  chucks,  which  are 
now  being  introduced  by  most  of  the  manufacturers,  they  seek 
to  make  change  of  chuck  bushing  easier.  All  these  half  chuck 
bushings  should  however  be  made  reversible,  end  for  end,  and 
be  reversed  once  a  week  by  the  miner,  to  equalize  wear  and 
keep  the  drill  point  true.  In  many  of  these  chucks,  unshanked 


146  ROCK  DRILLS 

i-in.,  1-in.,  or  IJ-in.  octagon  steel  can  be  used,  saving  expense 
of  shanking.1 

Feed-screws  and  Nuts.  —  All  feed-screws,  feed-nuts,  handles, 
etc.,  should  be  kept  in  order  and  replaced  when  worn.  A  stand- 
ard system  of  special  nuts  should  be  introduced  and  fitted  to 
the  feed-screws  as  they  wear.  This  last  recommendation  is  well 
worth  attention  as  tending  to  minimize  the  lost  motion  so  notice- 
able when  the  blow  is  struck,  with  a  worn  feed-screw. 

Joints.  —  All  joint  faces  should  be  kept  straight  and  true,  and 
if  necessary  scraped  up  to  a  bearing  by  the  aid  of  a  surface  plate 
kept  for  the  purpose. 

Test  for  Air  Tightness.  —  On  securing  the  piston  at  mid- 
stroke,  turn  air  on  full.  Air  should  not  escape  anywhere.  A 
machine  should  not  be  sent  out  of  the  shop  unless  it  complies 
with  this  test. 

Logging  Repairs.  —  Every  machine  must  be  sent  up  for  inspec- 
tion once  in  ten  weeks.  Each  machine  should  be  marked  with  a 
number;  all  inspections  and  repairs  should  be  logged  against  this 
number,  giving  the  date  and  details  of  work  done  on  it. 

Standards.  —  In  renewing  the  various  parts  throughout  the 
machines,  standard  sizes  must  be  adopted  and  adhered  to  as 
closely  as  possible,  consistent  with  working  conditions,  that  the 
various  parts  may  be  interchangeable. 

Bars.  —  All  necessary  repairs,  alterations,  and  renewals  must 
be  made  by  using  the  best  quality  of  standard  fittings  and  the 
heaviest  quality  of  steel  pipes. 

Clamps  and  Arms.  —  The  bolts  must  be  kept  in  perfect  order. 

Jacks  and  Jack  Stools.  —  Jack  screws  and  nuts  with  proper 
tightening  bars  must  be  kept  in  good  order.  Where  separate, 
jack  stools,  having  a  wooden  block,  are  used,  these  blocks  must 
be  renewed  when  required. 

Fitted  Up  Spares.  —  Not  less  than  two  complete  machines, 
two  clamps,  two  arms,  two  jack  stools,  six  tightening  bars,  two 
valve  chests,  and  all  smaller  details  in  greater  proportion  must 
be  always  available. 

Machine  Connections.  —  All  machines  sent  into  the  mine  must 

1  The  head  of  the  drill-shank  gradually  eats  into  the  chuck  at  the  end  of 
the  bushing.  Drills  should  be  tested  for  this  whenever  they  come  up  and 
steel  buttons  inserted  into  the  hole.  The  latest  practice  of  enlarging  drill 
shanks  tends  greatly  to  reduced  wear  on  both  shank  and  bushings. 


MAINTENANCE  OF  ROCK  DRILLS  147 

be  provided  with  spuds  for  hose-coupling.     The  latest  practice 
is  to  use  screws  with  three  or  five  threads  to  inch. 

MAINTENANCE  OF  HAMMER  DRILLS 

The  notes  with  regard  to  piston  drills  apply  in  their  general 
principles  to  hammer  drills.  The  effects  of  wear  are  mojre  often 
shown  by  sudden  breakages.  Pistons,  hammers,  and  cylinders 
are  generally  renewed  entirely  when  worn.  The  vibrations  set 
up  and  the  severe  stresses  induced  by  repeated  blows  at  high 
velocity  tend  to  crystallize  cylinders,  drills,  pistons,  and  anvil 
blocks.  In  those  machines  which  do  not  employ  separate  valve, 
anvil  block,  striking  pin,  or  tappet,  but  which  strike  the  steel 
direct,  it  is  obvious  that  particles  of  grit  can  enter  the  cylinder. 

This  is  especially  true  when  drilling  dry  up-holes  and  when 
the  machine  is  laid  aside.  The  drill  repairer  should  always  care- 
fully examine  the  interior  of  the  cylinder  for  undue  wear  due  to 
this  cause.  In  machines  using  water  injection,  corrosion  in  the 
interior  of  machine  or  in  the  chuck  is  to  be  guarded  against. 

A  mine  using  rock  drills  should  employ  a  fitter  who  has  been 
properly  trained  for  the  work.  He  ought,  in  addition,  to  be  sent 
below  to  learn  to  operate  a  machine  so  that  he  will  then  know 
where  to  look  for  wear  and  leakage.  When  a  machine  comes  up 
from  below  it  is  usually  coated  with  rust,  and  the  feed-screw  nut 
is  covered  with  grease  and  grit.  This  should  be  removed  at 
once  so  that  all  wear  or  defects  become  apparent.  A  tank  of 
caustic  soda  heated  by  steam  may  be  found  a  useful  adjunct  to 
the  drill  shop.  Ratchet  and  piston  springs  should  be  changed 
every  time  the  machine  comes  up.  This  will  pay  for  itself  as  a 
safeguard  against  failure  by  wear  or  loss  of  elasticity. 

Testing.  —  Outside  the  shop,  or  inside  if  there  is  space,  a 
clamp  should  be  firmly  mounted  either  on  a  bar  embedded  between 
two  heavy  ferro-concrete  columns  sunk  in  the  ground,  or  some 
other  arrangement  giving  a  rigid  support.  At  a  convenient  dis- 
tance is  another  column,  rigidly  erected,  and  protected  by  an 
iron  plate.  This  is  to  be  used  to  try  the  drills  on.  The  repaired 
machine  can  then  be  mounted  and  connected  with  a  surface  pipe 
leading  from  the  air  compressor,  and  be  tested  by  inserting  a 
blunt  drill  set  to  run  against  either  the  iron  plate  or  a  piece  of 
heavy  spring  steel  securely  attached  to  the  column. 

Indicator  Cards.  —  The  indicating  of  a  rock  drill  should  be 


148  ROCK  DRILLS 

insisted  upon  before  the  drill  is  passed  as  fit  for  work.  The  dia- 
grams require  some  experience  in  reading.  One  of  the  most 
important  points  to  examine  them  for,  in  those  drills  which  profess 
to  strike  a  free,  dead,  uncushioned  blow,  is  to  see  that  they  actually 
do  so.  If  back  pressure  is  shown  the  cause  must  be  found  and  the 
remedy  applied.  Later  experiments  have  made  me  of  the  opin- 
ion that  in  practice  no  drills  strike  a  really  free  blow.  There  is 
always  some  sustaining  action  —  owing  to  the  rapid  boring 
recently  exhibited  by  drills  which  cushion,  such  as  the  Chersen 
and  Siskol.  The  importance  of  this  feature  in  ground  of  mod- 
erate hardness  is  apt  to  be  exaggerated.  In  many  types  of  drills 
wire  drawing' at  full  speed  is  very  evident.  This  is  often  due  to 
too  small  a  hose  being  employed  to  supply  air.  A  1-in.  hose  in 
50  ft.  lengths  does  not  properly  supply  a  3j-in.  machine,  and 
when,  as  always  happens,  this  hose  gets  broken  and  has  to  be 
mended  with  pieces  of  f-in.  pipe  the  trouble  becomes  much  worse. 
Again,  when  dents  are  made  in  it  the  effective  area  is  reduced. 
A  few  leaks  due  to  carelessly  made  connections  at  the  machine 
and  pipe  line  cut  down  the  amount  of  air  so  that  quite  a  number 
of  machines  are  really  not  getting  more  than  half  the  air  they 
should.  This  subject  of  air  hose  and  pipe  lines  is  dealt  with  in 
another  place,  but  since  the  up-keep  of  machines  includes  that  of 
hose,  the  question  is  taken  up  here. 

Boring  Out  Cylinders.  —  Another  matter  arises.  Does  it  pay 
to  bore  out  rock-drill  cylinders  as  just  described?  The  answer  to 
this  question  depends  on  the  relative  value  that  must  be  given 
to  certain  factors,  i.e.,  cost  of  machines,  repairs,  labor,  and  com- 
pressed air.  In  general,  I  doubt  very  much  if  it  does  pay  to 
bore  out  rather  than  buy  new  cylinders.  Recently  some  remark- 
able and  useful  tests  were  made  at  the  Meyer  &  Charlton  mine. 
Mr.  E.  J.  Laschinger  has  given  the  results  in  a  paper  read  before 
the  South  African  Association  of  Engineers.  These  tests  deal 
with  the  consumption  of  air  by  old  and  new  rock  drills.  Fourteen 
Ingersoll  rock  drills,  3J  in.  (original)  in  diameter  were  thoroughly 
overhauled.  Some  of  these  machines  had  been  working  four 
years!  Their  air  consumption  was  compared  with  that  of  14 
new  Ingersoll  drills.  At  64.2  Ib.  surface  pressure  they  used  59.7 
per  cent,  more  air  per  inch  drilled  than  the  new  machines,  and 
their  drilling  speed  was  eleven  per  cent.  less.  These  drills  had 
been  in  a  worse  condition  before  the  trial  and  used  probably  80 


MAINTENANCE  OF  ROCK   DRILLS  149 

per  cent,  more  air.  The  cost  of  air  per  rock  drill  per  shift  would, 
with  new  machines,  amount  to  about  10s.  per  shift.  Here 
then  it  is  evident  that  it  would  have  paid  over  and  over  again 
to  throw  away  all  the  air- wasting  parts  of  the  old  machines,  i.e., 
pistons,  cylinders,  valves,  and  valve  chests,  and  buy  new  ones. 
On  the  Rand,  machines  are  sold  from  £20  to  £25,  and  cylinders 
cost  about  £4  10s.  Od.  It  costs  nearly  15s.  to  rebore  a  cylinder. 
On  other  fields  circumstances  might  be  different.  We  will  sup- 
pose, however,  that  a  manager  has  decided  that  a  3-in.  machine 
strikes  a  blow  heavy  enough  to  give  the  maximum  boring  speed 
(with  the  air  pressure  decided  upon  and  supplied  by  his  com- 
pressor) in  the  rocks  met  with  in  his  mine.  He  runs  as  many 
rock  drills  as  his  compressor  will  allow.  Suppose  now  he  bores 
out  both  cylinders  and  valve  chests  and  buys  larger  pistons  to 
suit  them.  He  puts  this  off  to  the  last  minute  and  consequently 
runs  his  machines  with  slack  pistons  for  some  time,  losing  air  by 
leakage.  When  he  has  bored  out  his  cylinders,  each  drill  uses 
far  more  air  than  before.  It  either  strikes  a  harder  blow  than 
necessary,  or  owing  to  the  greater  demand  on  the  compressor  the 
pressures  must  be  lowered  and  the  rate  of  boring  of  the  other 
drills  falls  off. 

There  are  so  many  experimentally  unsolved  problems  in  regard 
to  rock-drill  work  that  it  is  impossible  to  make  this  discussion 
complete.  Some  contend  that  it  pays  better  to  use  a  low  pressure 
of  say  60  lb.,  and  use  larger  machines.  This  is  the  view  that 
was  until  recently  held  largely  in  South  Africa.  Others  believe 
in  high  pressures  and  smaller  machines.  This  is  the  American 
practice,  and  it  seems  to  me  the  right  one. 


IX 


DRILL  STEEL  AND   DRILL   BITS 

STEEL  is  the  name  given  to  iron  with  a  carbon  contents  of 
0.3  to  2.0  per  cent.  It  merges  on  the  lower  percentage  into 
wrought  iron  and  on  the  higher  into  cast  iron.  Steel  is  usually 
classified  into  different  tempers;  the  usual  temper  of  drill  steel 
being  from  0.5  to  0.875  per  cent,  carbon.  It  is  believed  that  when 
the  steel  is  heated  the  carbon  is  dissolved  in  it  somewhat  as  salt  is 
in  water.  If  the  steel  is  allowed  to  cool  slowly  there  will  be  a 
separation  of  cementite,  ferric  carbide  Fe3C,  dependent  on  the 
percentage  of  carbon.  The  mass  is  then  no  longer  homogeneous. 
From  a  microscopic  examination  the  carbon  alloy  or  compound 
appears  in  the  steel  like  a  network.  If  the  steel  is  cooled  quickly 
there  is  no  time  for  crystallization,  and  the  carbon  remains  evenly 
distributed  in  the  body  of  the  steel.  The  more  carbon  the  steel 
contains  the  easier  it  is  to  harden;  but  the  hardness  does  not 
depend  on  the  percentage  of  carbon  present,  but  on  the  temper- 
ature from  which  it  is  cooled.  If  this  hard  and  brittle  metal  is 
heated  at  a  temperature  of  350  to  580°  F.,  its  hardness  is  slightly 
reduced  and  the  brittleness  largely  removed.  This  process  is 
called  tempering.  The  temperature  applied  must  remain  within 
certain  limits  for  each  grade  of  steel.  The  maximum  color  and 
temperature  suitable  for  each  grade  is  given  in  the  accompanying 
table. 

TABLE  SHOWING  COLOR  OF  STEEL  AT  VARIOUS  TEMPERATURES 


Per  cent.  Carbon 

Color  of  Heated  Bar 

Corresponding  Temperature 
Deg.  C. 

1.5 
1.25 
1.125 

Cherry  red 
Bright  red 
Red 

800 

825 
850 

1.00 

Full  red 

875 

0.875 
0.75 

Bright  red 
Full  bright  red 

900 

150 


DRILL   STEEL  AND   DRILL   BITS  151 

For  every  50°  C.  above  these  temperatures  the  tools  made  suffer 
in  efficiency  4  to  5  per  cent.  Steel  used  in  rock  drilling  has  to 
withstand  severe  stresses,  perpetual  vibration,  and  tends  to  set 
up  crystallization.  It  must  be  able  to  present  a  cutting  edge 
to  the  rock  as  hard  or  harder  than  the  rock  itself. 

In  America  drill  steel  is  used  containing  as  high  as  one  per 
cent,  carbon.  The  tendency  is,  however,  to  use  steel  containing 
lower  percentages.  This  steel  has  to  be  most  carefully  heated,  for 
as  already  shown  the  higher  the  carbon  contents,  the  lower  the 
temperature  at  which  the  danger  of  " burning"  or  the  oxidation 
of  the  combined  carbon  must  begin.  High-carbon  steel  is  harder 
in  the  bar  than  lower  tempers,  and  when  working  in  very  hard 
ground  it  will  stand  where  softer  steels  will  bend.  High-carbon 
steels  are  hard  to  weld  satisfactorily  as  the  steel  burns  when 
raised  to  the  welding  heat. 

DRILL  BITS 

A  drill  bit  consists  of  the  shank  or  portion  inserted  in  the 
chuck  of  machine,  the  shaft,  and  the  bit  or  cutting  edge  formed 
with  a  shoulder  or  spread  to  allow  of  clearance  in  the  hole.  This 
cutting  edge  becomes  worn  away  and  blunted  in  cutting  the  rock. 
It  must  be  re-formed  by  forging  the  heated  steel.  Each  one  of  a 
set  of  drills  to  bore  a  hole  has  a  diminished  diameter,  length,  or 
gage  of  cutting  edge  or  edges,  for  as  the  bit  wears  away  the  hole 
becomes  smaller  in  diameter. 

Heating  Drills.  —  Drill  bits  should  have  any  mud  or  clay 
removed  before  being  heated.  They  are  treated  in  ordinary 
blacksmith  forges  with  charcoal,  coal,  or  coke.  Sometimes  the 
forges  are  built  in  special  shapes  like  long  boxes,  with  the  air 
supply  distributed  along  them  in  such  a  manner  that  only  the 
ends  of  drills  are  heated.  Gasoline  or  oil  burning  forges  are 
employed  in  the  drill-sharpening  shops  at  the  Komata  Reefs 
mine,  New  Zealand,  and  in  many  mines  on  the  Rand.  In  such 
forges  the  supply  of  gasoline  can  be  regulated  so  that  all  danger 
of  overheating  the  steel  is  removed.  One  2J-in.  Gary  burner  is 
used  for  each  furnace.  The  gasoline  is  used  at  25-lb.  pressure; 
the  consumption  is  stated  to  be  about  10  gal.  per  8-hr,  shift. 
About  2700  hand  drills  are  sharpened  in  two  shifts  by  three  men 
on  each  shift  when  using  these  forges. 

Electric  forges  or  heating  furnaces  are  now  being  tried  for 


152 


ROCK   DRILLS 


underground  work  on  the  Witwatersrand  gold  fields.  They  are 
constructed  to  heat  four  large  drills  at  a  time  in  an  electrolyte. 
The  temperature  is  thoroughly  under  control  and  the  bath  is 
evenly  heated.  It  is  possible  to  heat  only  a  short  length  of  the 
drill  at  the  bit.  This  furnace  has  not  proved  popular  for  this 
work  and  oil  furnaces  are  largely  employed  in  underground 
sharpening  shops. 

The  A.  E.  G.  electric  furnace,  forms  an  entirely  original  design, 


FIG.  90.  —  Vertical  section. 

and  Figs.  90  and  91  show  elevation  and  plan  of  the  furnace,  con- 
sisting of  a  heat-resisting  crucible  in  the  center,  surrounded  by 
a  layer  of  asbestos,  the  whole  embedded  in  brickwork  enclosed  in 
a  cast-iron  frame.  Two  electrodes  of  soft  iron  are  placed  at 
opposite  sides  of  the  crucible  and  the  electric  current  is  taken 
to -the  same  from  the  secondary  of  a  transformer.  A  certain 
quantity  of  a  metallic  salt  -is  filled  in  the  crucible,  which  when 
melted  forms  a  conductor  between  two  electrodes. 


DRILL   STEEL  AND   DRILL   BITS 


153 


The  two  electrodes  form  the  contacts  and  the  bath  is  heated 
by  the  passage  of  the  current.  By  increasing  or  decreasing  the 
current  the  bath  is  given  any  desired  temperature,  and  as  there 
is  no  radiation,  owing  to  its  good  heat-insulating  properties  — 
with  the  exception  of  the  top  surface  which,  however,  can  also 
be  closed  up  by  means  of  the  lid  —  the  temperature  is  in  practice 
as  evenly  distributed  in  the  whole  of  the  bath  as  can  be  theoreti- 


n 


FIG.  91.  —  Horizontal  section.     Electric  heating  furnace  of 
Allegamine  Electrictats  Geschift. 

cally  expected.  Owing  to  radiation,  the  top  layer  will  have  a 
slightly  lower  heat  than  the  bottom  layers,  but  the  difference  is 
not  more  than  15°  C.,  or  1J  per  cent. 

High-carbon  steel  must  not  be  heated  above  a  clear  red  color, 
and  in  an  ordinary  forge  care  must  be  taken  that  the  bits  are  well 
covered  by  the  fuel.  The  blast  should  not  impinge  directly  on 
one  drill  or  parts  of  it,  causing  local  overheat.  The  drills  should 


154  ROCK  DRILLS 

be  constantly  turned  in  the  fire.  Owing  to  the  need  of  heating 
and  tempering  different  steels  in  different  ways,  blacksmiths 
should  be  given  one  grade  of  steel  only  to  work  with  if  satisfac- 
tory results  are  to  be  obtained.  If  special  quality  steel  be  used 
for  extra  hard  ground  in  a  mine,  or  for  severe  work,  such  as  putting 
in  all  dry  holes,  some  special  manner  of  distinguishing  the  steel 
should  be  employed  so  that  it  can  be  treated  separately. 

Tempering.  —  As  before  stated  the  degree  of  hardness  of  the 
cutting  edge  depends  on  the  temperature  of  the  steel  at  the  mo- 
ment it  is  quenched  in  water.  At  about  440°  F.,  the  drill  steel  is 
tinged  with  yellow  and  when  quenched  in  water  the  color  is  gray- 
ish white.  This  color  shades  off  to  the  full  blue  temperature 
of  600°  F.,  used  for  tempering  saws  and  springs.  With  high- 
carbon  steels  the  chisel  bit  is  first  formed,  then  the  steel  is 
reheated  and  plunged  in  water  for  a  moment;  the  surface  of  the 
drill  is  rubbed  on  a  stone  and  the  line  of  colors  is  seen  advancing 
down  towards  the  cutting  edge;  yellow  straw  color  in  front  fol- 
lowed by  blue;  as  thS  yellow  reaches  the  end,  the  bit  is  plunged 
in  cold  water.  Sometimes  acid,  salt,  rape  seed,  oil,  or  coal  tar 
is  added  to  the  bath  to  make  cooling  quicker  or  slower.  The 
presence  of  a  salt  dissolved  in  water  increases  its  conductivity. 
To  save  time  in  watching  the  colors  the  drills  may  be  placed  in 
a  bath  of  3  parts  lead,  and  1  part  tin,  kept  just  molten  at  a  tem- 
perature of  440°  F.  They  may  then  be  plunged  when  convenient. 
Most  steel  bits  used  for  rock  drills,  after  sharpening,  are  placed 
upright  on  a  grating  which  is  half  an  inch  below  the  surface  of  water 
in  a  tank  constantly  supplied  with  cool  water.  The  cutting  edge 
is  alone  chilled  and  the  rest  of  the  bit  cools  slowly.  High-carbon 
steels  are  in  danger  of  ringing  or  cracking  near  the  edge  of  the 
water  if  placed  in  the  water  at  any  but  the  exact  temperature. 
If  the  temperature  is  too  low  they  are  soft.  Where  many  hun- 
dreds of  drills  have  to  be  sharpened  daily  it  is  impossible  to  give 
each  one  great  attention,  especially  when  unskilled  labor  is  em- 
ployed in  attending  to  the  forge  and  assisting  in  work  which  is 
usually  as  on  the  Rand,  done  on  contract.  These  considera- 
tions have  led  to  the  evolution  of  two  different  systems  of  working 
with  drill  steel,  which  for  convenience  I  will  call  the  American 
and  South  African  systems. 

American  System  of  Drill  Bits.  —  Octagon,  hexagon,  or  round 
steel  of  high-carbon  contents  is  employed.  Bits  of  star  section 


DRILL  STEEL  AND   DRILL    BITS 


155 


are  forged  from  the  solid  bar  by  jumping  up  and  splitting  in 
sharpening  machines,  or  by  hand.  This  type  is  shown  in  Fig.  92, 
taken  from  the  Sullivan  catalogue.  These  drills  are  reheated 
after  sharpening  and  properly  tempered.  There  are  no  welds  to 
give  trouble  by  breakage  in  very  hard  ground;  the  shaft  of  the 
steel  has  ample  clearance  in  the  hole;  there  is  plenty  of  shoulder 
on  the  drill  to  kick  back  the  cuttings.  They  are  expensive  in 
first  cost  and  sharpening;  and  if  welding  is  not  practised,  where 


FIG.  92.  —  Sullivan  rock-drill  bits. 


the  short  lengths  cannot  be  sold  or  used  again  in  some  other 
way,  there  is  great  waste  of  steel. 

South  African  System  of  Drill  Bits.  —  For  star  bits  pieces,  of 
star  or  cruciform  section  steel  containing  0.5  to  0.6  per  cent, 
carbon,  are  welded  on  to  cheap  low-carbon  shank  steel  of  IJ-in. 
diameter,  octagon  section.  For  starters  the  star  or  cruciform 
steel  is  forged  down  half  its  length  under  the  steam  hammer  to 
form  a  shank  and  shaft.  The  steel  of  0.5  to  0.6  per  cent,  carbon 
can  stand  a  much  higher  heat  in  the  forges  without  damage,  and 
as  natives  are  employed  to  tend  fires  this  is  necessary.  Steels 
are  sharpened  and  plunged  at  just  whatever  heat  there  may  be 
when  the  sharpening  is  finished.  Cruciform  bits  are  placed  on 
the  rack  in  a  tank  already  described.  Undoubtedly  much  steel 
gets  overheated  and  its  hardness  spoiled.  The  steels  are  never 
allowed  to  anneal  or  soften.  They  are  always  hard.  The  large 


156  ROCK   DRILLS 

number  of  drills  to  be  dealt  with  renders  the  adoption  of  the 
American  system  difficult. 

Overheating.  —  It  will  be  seen  that  the  chief  danger  to  be 
guarded  against  is  overheating.  The  adoption  of  a  suitable  elec- 
tric furnace,  oil  furnace,  or  a  gas-fired  reverberating  furnace  in 
which  the  heat  could  be  kept  under  good  control  would  be  a  great 
step  in  advance  and  is  being  attempted.  Coke  furnaces  of  spe- 
cial design  are  used  in  Kalgoorlie.  So  mere-heating  bath  or 
electric  furnace  should  also  be  introduced  to  allow  drills  to  be 
quenched  at  exactly  the  right  temperature.  It  cannot  be  too 
emphatically  insisted  upon  that  successful  rock-drill  work  de- 
pends as  much  as  anything  on  drills  being  of  exact  standard  cut- 
ting ends,  straight  in  the  shaft  and  shank,  of  the  right  hardness  and 


FIG.  93.  —  Special  blacksmith's  tools. 

toughness.  In  the  shop  a  rock  drill  should  be  set  up,  provided 
with  a  new  chuck  and  bushing,  and  periodically  all  drills  should 
be  tested  for  alignment  and  wear  on  shanks,  by  placing  drills  in 
chuck  and  rotating. 

Sharpening  Chisel  Bits.  —  If  the  corners  are  badly  worn  the 
smith  lays  it  on  the  anvil,  upsets  or  blunts  it,  driving  the  material 
back  to  give  the  proper  width.  Then  the  drill  is  held  on  the  anvil 
at  a  slope  of  about  1:2;  if  long  machine  chisels  are  being  sharp- 
ened the  shank  end  is  laid  in  a  hanging  rest  to  support  it.  The 
edge  of  the  bit  is  held  even  with  the  anvil  and  is  hammered  until 
a  new  cutting  edge  is  formed  and  the  shoulders  if  necessary  drawn 
out.  The  final  blows  should  be  light  and  glancing  to  draw  the 


DRILL  STEEL  AND   DRILL   BITS 


157 


steel  fibers  towards  the  cutting  edge.  The  width  of  each  bit  is 
then  gaged  and,  if  necessary,  corrected. 

Sharpening  Cruciform  Bits.  —  For  making  and  dressing  the 
drill  steel  bits,  the  blacksmith  uses  a  set  of  tools  which  are  shown 
in  Fig.  93.  The  shape  of  the  bit  may  be  either  X  or  +,  deter- 
mined by  the  kind  of  rock.  The  special  tools  are:  No.  27^  dolly 
X;  No.  28,  dolly  +;  No.  29,  top  splitting  tool;  No.  30,  bottom 
splitting  tool;  No.  31,  set  hammer;  No.  32,  top  shank  swage; 
No.  33,  bottom  shank  swage,  and  No.  34,  sow. 

It  is  a  good  plan  to  have  a  separate  dolly  for  each  sized  bit, 
with  the  exact  gage  marked  off  on  each. 

MACHINE  SHARPENERS  FOR  DRILL  STEEL 

Some  hand  sharpening  is  very  good  and  some  very  bad.  The 
advantages  of  having  a  machine  that  will  do  this  work  more 


FIG.  94.  —  Word  drill  maker  and  sharpener. 

rapidly  and  uniformly  has  led  to  the  introduction  of  numerous 
machine  sharpeners.  Of  these  the  best  known  in  America  is 
the  Word  and  the  Ajax,  Fig.  94,  shows  the  Word  which  consists  of 
two  air-driven  hammers,  one  vertical  and  one  horizontal.  This 
and  the  Numa  sharpener,  is  working  in  quite  a  number  of  Ameri- 
can mining  fields.  These  machines  are  used  to  forge  up  star 
bits  from  the  solid  bar  as  well  as  to  sharpen  steel. 


158 


ROCK  DRILLS 


On  the  Rand,  drill  sharpeners  of  similar  design  have  not 
apparently  been  able  to  compete  with  hand  sharpening. 

Dunstan's  Drill  Sharpener.  —  A  new  drill  sharpener  Fig.  96, 
invented  by  Nicholas  Dunstan,  is  being  placed  on  the  market  by 
the  Tuckingmill  Foundry  Company,  of  Canborne,  Cornwall.  The 
machine  consists  of  two  forging  hammers  mounted  horizontally 
on  a  side  bed  side  by  side,  with  corresponding  dies  held  in  boxes 
on  the  bed. 

The  hammers  are  operated  by  compressed-air  cylinders,  shown 


FIG.  96.  —  Elevation  and  plan  of  Dustan  drill  sharpener 


in  the  accompanying  section  and  elevation  at  A  and  A1 '.  The 
piston-rods  B  and  E'  carry  tool  holders  H  and  H',  at  the  end  of 
which  are  inserted  the  forging  dies  K  and  K '.  The  stationary 
die  boxes  are  shown  at  DD'  and  the  stationary  dies  at  J  and  J7 
The  cylinder  A  is  used  for  upsetting  the  bar,  which  is  held  in  line 
with  the  piston-rod  B.  Two  clamps  are  used,  E  and  G,  the  former 
to  hold  the  bar  in  position,  and  the  latter  to  hold  the  dies  /  up 
in  close  contact  with  the  end  of  the  bar.  The  position  of  the 
cylinder  A  can  be  varied  longitudinally  by  means  of  the  handle 


DRILL  STEEL  AND   DRILL  BITS  159 

P  and  gear  QRS,  while  the  position  of  the  bar  between  the  dies 
is  adjusted  by  a  stop,  which  is  not  shown  in  the  illustration. 

The  cylinder  A'  is  used  for  cutting  out  wings  and  flattening 
them,  the  bar  being  held  at  right  angles  to  the  piston-rod  B' ',  as 
indicated  by  the  arrow  F.  . 

When  a  chisel  bit  is  to  be  forged  out  of  a  new  bar,  or  an  old 
one  reshafpened,  it  is  first  held  at  F  and  a  few  blows  given  be- 
tween J'  and  Kf  to  flatten  it  out.  It  is  then  inserted  in  the  other 
side  of  the  machine  at  X  and  a  few  blows  between  /  and  K  put 
on  a  cutting  edge. 

The  forming  of  a  cross-shaped  bit  takes  three  operations. 
The  bar  is  first  placed  at  X  and  the  end  jumped  up,  with  a  slight 
cross  indentation  over  the  top.  It  is  then  transferred  to  the 
position  F  and  split  into  wings.  By  holding  the  wings  to  the 
outer  edge  of  the  die  they  are  further  flattened  out  at  the  edges. 
The  bar  is  then  brought  back  to  the  other  side  of  the  machine 
and  a  few  blows  of  the  piston-rod  B  put  on  a  working  edge. 

If  a  cross-shaped  bit  is  being  re-sharpened,  it  is  not  necessary 
to  insert  it  in  the  dies  JK,  so  the  first  operation  required  in 
forging  a  new  bar  is  dispensed  with.  It  is  only  necessary  to  cut 
out  the  wings  and  flatten  them  at  F  and  put  on  the  cutting  edge 
at  X. 

In  working  the  upsetting  cylinder  it  is  necessary  to  hold  the 
bar  tightly  in  two  clamps.  When  working  the  other  cylinder 
the  bar  is  held  in  position  by  the  smith,  without  the  aid  of  clamps. 
It  is  understood,  of  course,  that  different  dies  are  required  for 
the  first  operation  of  upsetting  the  bar  and  the  final  one  of  putting 
on  a  cutting  edge  when  working  the  cylinder  A.  Also  different 
dies  are  required  when  making  cross-shaped  bits  and  chisel  bits. 
Different  sets  of  dies  are  required  according  to  the  diameter  of 
the  bars  treated.  In  dealing  with  new  bars  when  making  cross- 
shaped  bits,  it  is  desirable  to  make  a  large  number  at  once,  first 
giving  all  the  bars  the  preliminary  upset,  then  changing  the  dies, 
and  conducting  the  second  and  the  parts  of  their  operation.  The 
second  and  third  can  be  done  at  one  heat,  as  can  also  the  two 
operations  in  making  a  chisel  bit. 

The  labor  required  in  working  the  machine  includes  a  smith 
and  a  boy,  with  one  or  two  boys  to  bring  the  bars  from  the  fire. 
The  boy  helping  to  work  the  machine  attends  to  the  admission 
and  cut-off  of  the  compressed  air,  and  tightens  up  one  of  the 


160 


ROCK   DRILLS 


clamps  G.  In  no  part  of  the  operation  is  any  steel  cut  to  waste. 
The  formation  of  the  cutting  edge  is  done  by  an  upsetting  process 
which  obviates  loss  of  steel,  and  also  tends  to  make  the  cutting 
edge  stronger. 

The  makers  claim  that  the  machine  will  forge  50  new  chisel 
bits  from  the  bar  in  an  hour,  and  sharpen  from  100  to  150  old 
ones.  Also  that  20  new  cross-bits  can  be  forged  from  the  bar  in 
an  hour,  and  from  80  to  100  re-sharpened  in  the  same  time. 

Kimber  Sharpening  Machine.  —  A  machine  for  making  or 
sharpening  rock  drills  or  drill  bits.  It  has  two  sets,  b  and  c,  of 
forging  and  swaging  tools,  Fig.  98,  the  latter  being  rounded  and 
tapered  and  the  former  L-shaped;  the  tools  are  mounted  in  radial 


FIG.  97.  —  Kimber  drill  sharpening  machine. 

guides  a6  in  a  disc  a2,  which  is  fixed  to  the  frame  A,  Fig.  97.  The 
tools  are  held  in  position  by  a  ring  a7,  within  which  are  slots  fr2, 
engaging  pins  bl  in  the  tools,  each  set  of  which  is  alternately 
pressed  inwards  against  the  action  of  springs  64  by  rollers  D 
mounted  on  an  oscillating  ring  C  engaging  projecting  ends  c1  of 
the  tools.  When  the  ring  is  in  the  position  shown,  the  tools  are 
held  out  of  action,  and  the  actuating  mechanism  is  put  out  of 
gear.  The  ring,  which  is  formed  of  two  annular  pieces  connected 
by  webs  c3,  may  be  actuated  by  an  oscillating  cylinder  mounted 
on  the  bed-plate  A,  Fig.  97.  Some  means,  such  as  a  hand-operated 
bell-crank  lever  and  rod,  is  used  to  control  the  valve.  To  allow 
of  sharpening  drills  of  different  sizes,  the  movement  of  the  ring 
is  limited  by  a  stop  on  the  ring  contacting  with  two  stops,  which 
project  at  one  end  from  lugs  fixed  to  the  disc  a2,  and  at  the  other 


DRILL  STEEL  AND   DRILL   BITS 


161 


end  are  provided  with  spring  buffers  and  adjusting  screws. 
To  lubricate  and  cool  the  forging  tools  and  swages,  and  for  re- 
moving the  scale  from  between  them,  a  pipe  o3,  Fig.  97,  connected 
with  a  supply  of  compressed  air  and  with  an  oil  cup  o5  and  cock  o6, 
is  joined  to  a  ring  o  fixed  to  the  disc  a2,  which  has  an  annular 
groove  o1  connected  by  holes  o7  with  grooves  p,  pl,  p2  in  the  guides 
a6  and  plate  a7.  The  dolly  j  for  forming  the  radial  cutting  edges 
is  pressed  against  the  "drill  by  a  spring  j1  when  in  operation,  but 
may  be  drawn  back  by  a  handle  f  having  a  trigger  fitting  in  a 
notch  in  the  quadrant  f  and  being  connected  to  a  rod  j1,  fitting 
round  a  hook  on  the  dolly.  The  dolly  is  actuated  by  the  striker 
h  of  a  hammer  H.  The  end  of  the  drill  is  held  in  a  recess  in  a 


FIG.  98.  —  Swaging  tools  for  Kimber  sharpener. 


carriage  k1  moved  on  parallel  rails  A;  by  a  handle  m3,  and  finally 
adjusted  in  position  by  a  half-nut,  which  is  mounted  in  a  piece 
depending  from  the  carriage  and  is  kept  in  contact  with  the  screw 
m  by  a  wreight  M  on  a  lever  k7  with  a  disengaging  handle  fc9.  The 
screw  is  rotated  by  a  hand-wheel  m6,  and  bevel  gearing.  A  self- 
centering  vice  or  holder  for  the  drill  comprises  two  jaws  n,  Fig. 

97,  mounted  on  projections  from  two  nuts  ?,  which  engage  a  right 
and  left-handed  screw  I2,  in  bearings  at  the  end  of  the  table  and 
rotated  by  a  hand-wheel  J8  through  spur  gearing.     Tools  s,  Fig. 

98,  for  bringing  up  the  corners   of   the  wings    and  for  roughly 
forming  the  radial  cutting  edges,  afterwards  forged  and  dollied, 
are  mounted  on  the  bed-plate,  and  comprise  a  striker  R  and  a  die 
block  r.     The  striker,  which  is  operated  by  a  piston  tl,  has  a  shoul- 
der v2  normally  pressed  against  the  cylinder  by  two  springs  v 


162  ROCK  DRILLS 

attached  to  the  tool  and  the  cylinder  by  projections.  The  tool 
is  beveled  and  has  a  slightly  concave  and  fluted  striking  face  and 
an  intermediate  groove  r1.  The  die  block  r  is  grooved,  to  receive 
concave  dies  s1  of  different  thicknesses  according  to  the  size  of 
drill,  having  projections  s2  fitting  in  holes  s  in  the  block.  These 
dies  s1,  which  reduce  the  radial  length  of  the  wings  of  the  drill, 
are  of  such  length  that  the  side  wings  do  not  rest  on  the  upper 
surface  of  the  block. 

This  machine  being  designed  for  use  on  the  Rand,  where  welded 
bits  are  employed,  is  designed  for  sharpening  steel,  of  star  (cru- 
ciform) section.  It  is  designed  to  forge  or  draw  the  bit  by  a 
kneading  action.  Several  of  these  machines  are  now  at  work, 
one  for  two  years.  This  machine  will  sharpen  from  1200  to 
1800  drills  per  shift.  Sharpening  machines  are  subjected  to 
severe  wear  and  require  close  attention  and  careful  usage.  Where 
a  large  number  of  drills  have  to  be  dealt  with  they  will  come  into 
use  more  and  more,  as  undoubtedly  better  work  can  be  done  by 
drills  whose  gage  and  length  of  wing  are  .mathematically  true. 

DESIGN  AND  SHAPE  OF  DRILL  BITS 

Nothing  will  be  more  puzzling  to  the  mining  student  than 
the  difference  noted  in  the  shapes  of  drill  bits  illustrated  in  vari- 
ous works  on  mining  and  in  various  catalogues.  This  difference 
is  partly  due  to  the  fact  that  differently  shaped  bits  are  suitable 
for  different  classes  of  rock  bored  and  for  different  directions 
and  depths  of  holes.  It  is  also,  however,  largely  due  to  want  of 
exact  knowledge  on  the  subject.  It  must  first  be  remembered 
that  with  piston  drills,  working  in  soft  rocks  or  rocks  that  break 
easily,  ejecting  the  broken  fragments  rapidly  has  more  effect  on 
the  rate  of  boring  than  merely  cutting  the  rock.  This  is  espe- 
cially true  in  cases  where  long  down-holes  are  bored.  It  is  in  ground 
such  as  this  that  drills  of  the  Leyner  type,  using  hollow  steel, 
show  to  such  advantage.  Where  the  ground  is  very  soft  the  bit 
need  not  be  sharp.  Unless  the  broken  rock  can  be  removed  by 
water  jets,  or  falls  out  of  the  hole  freely,  it  will  require  a  pro- 
nounced shoulder  on  the  drill  bit  to  kick  back  the  mud  on  the 
return  stroke. 

Where  the  rock  is  hard  the  angle  made  by  the  cutting  faces 
of  the  bit  must  not  be  too  sharp  or  they  are  liable  to  break.  The 
shoulders  must  be  well  supported  to  give  them  strength.  The 


DRILL  STEEL  AND   DRILL  BITS  163 

ejection  of  broken  rock  will  not  be  so  important,  relatively.  Other 
points  will  be  dealt  with  in  considering  the  various  illustrations. 

Chisel  and  Star  Bits.  —  It  will  be  seen  that  the  Sullivan  Drill 
Company  recommends  cross-bits  for  general  work,  Fig.  92. 
Australian  manufacturers  recommend  chisel  bits  for  all  work 
except  in  the  very  hardest  rock  after  the  hole  has  been  started. 
They  give  figures  to  show  that  in  certain  tests  held  in  Bendigo, 
Victoria  (size  of  bit  used  not  given),  18  cu.  ft.  of  air  per  foot 
drilled  was  used  with  star  bits  and  16.88  cu.  ft.  with  chisel  bits. 
These  measurements  were  taken  by  a  meter  and  are  scarcely 
reliable. 

In  soft  rock  chisel  bits  are  cheaper  to  make  and  sharpen.  They 
are  lighter  to  use,  have  more  clearance  in  the  hole  and  offer  less 
resistance  by  friction  to  the  turning  mechanism  of  the  drill.  They 
lose  their  gage  and  blunt  more  rapidly.  In  some  grounds  they 
bore  more  rapidly  than  cross-bits.  Star  or  cross-bits  have  the 
advantage  that  in  hard  ground  the  wear  on  the  cutting  edge  is 
halved  for  the  same  distance,  there  being  four  shoulders  to  ream 
out  the  hole.  These  allow  a  longer  distance  to  be  driven  on  a 
smaller  difference  of  gage  between  following  drills.  In  ground 
full  of  heads  and  fissures,  they  will  put  down  a  hole  where  a  chisel 
would  stick.  Mr.  Renmeaux  recommends  the  use  of  six-pointed 
bits.  Major  Derby  used  six-pointed  tubular  detachable  bits 
with  success.  Mr.  Anderson  advocates  bits  with  three  points, 
or  more  properly  cutting  edges.  Where  hollow  steel  is  employed 
bits  with  two  parallel  cutting  chisel  edges  prove  useful.  Holes 
can  be  started  with  them,  as  well  as  with  cross-bits. 

American  Practice.  —  The  best  summary  of  American  prac- 
tice in  shaping  bits  is  the  article  on  the  subject  in  the  Sullivan 
catalogue,  which  I  reproduce. 

"  For  general  mining  and  quarrying  purposes  the  ordinary 
cross-bit  is  recommended.  The  proportions  of  the  bit,  as  to 
length  and  thickness  of  the  wings  or  ribs,  are  indicated  in  the 
accompanying  illustrations,  1  to  4,  in  Fig.  92.  Nos.  1  and  2  are 
bits  for  hard,  non-gritty  rock,  and  are  alike  except  for  the  differ- 
ent angles  shown  on  the  cutting  edges.  No.  1  shows  about  the 
highest  angle  to  which  the  cutting  edge  can  be  made  without 
danger  of  breaking.  The  angle  shown  on  the  cutting  edge  in 
No.  2  is  one  of  many  which  may  be  used  under  different  condi- 
tions without  any  other  change  in  the  bit.  In  cutting  hard  and 


164  ROCK  DRILLS 

medium  hard  rock,  sharp  drills  and  a  wide-open  throttle  may  be 
used  to  good  advantage,  and  the  hole  will  not  ordinarily  clog 
with  mud,  as  the  amount  of  rock  loosened  by  each  blow  is  so 
little  that  it  is  at  once  mixed  into  slush  by  the  water  in  the  hole. 
The  sharp  rebound  of  the  drill  when  striking  hard  rock,  together 
with  the  positive  recovery  of  the  machine,  quickly  gets  rid  of 
this  slush.  If  the  same  bits  and  drill  are  run  on  an  open  throttle 
in  soft  or  even  medium  soft  ground,  the  hole  soon  becomes  clogged. 
The  reason  for  this  is  that,  while  the  hole  remains  of  the  same 
diameter,  and  the  amount  of  water  for  mudding  purposes  is  there- 
fore the  same,  the  steel  chips  out  three  or  four  times  as  much 
dust  at  each  blow  as  it  does  in  hard  rock.  The  rate  of  cutting 
should  therefore  be  reduced  in  order  to  keep  the  drill  working  at 
maximum  efficiency.  The  speed  may  be  regulated  by  throttling 
the  air  or  steam,  but  this  reduces  the  rapidity  of  action  of  the  drill 
so  that  it  does  not  always  mix  into  slush  the  dust  caused  even 
at  the  slower  speed.  The  recoil  of  the  steel  from  soft  rock  is 
also  considerably  less.  In  soft  rock  duller  bits  should  be  used, 
like  that  shown  in  No.  4.  The  angle  of  the  cutting  edge  may  be 
even  higher  than  this,  sometimes  almost  square  on  the  end,  in 
order  to  secure  good  results. 

"  In  connection  with  the  above  subject,  it  is  well  to  bear  in 
mind  the  length  of  the  wings  or  ribs  for  different  kinds  of  work. 
Nos.  1  and  2  show  an  extreme  length  for  very  hard  rock,  intended 
to  give  strength  and  hold  the  gage  as  long  as  it  is  necessary. 
Nos.  3  and  4  show  shorter  ribs,  which  give  the  bit  more  clearance 
and  make  it  more  desirable  for  general  purposes.  Under  ordi- 
nary conditions  its  ability  to  mix  mud  is  much  greater  than  that 
of  the  long  bit  like  No.  1.  For  drilling  dry  holes  in  tunnel  headings 
or  elsewhere,  the  bit  with  short  ribs  has  less  tendency  to  allow 
the  hole  to  draw  up.  The  wings  are  f  of  an  inch  thick  for  the 
size  shown  in  Nos.  1  to  4,  and  should  never  be  less  than  that  for 
this  size  of  bit  and  steel.  They  should  be  the  same  thickness 
throughout,  to  allow  free  return  of  the  cuttings.  If  gage  less 
than  2J  in.  is  desired,  make  the  bit  correspondingly  shorter. 

"  In  seamy  ground,  the  bit  shown  in  No.  5  will  occasionally 
work  satisfactorily  when  a  cross-bit  would  not  prevent  a  "rifled" 
hole,  since  the  "X"  bit  strikes  only  half  as  often  as  the  "-f-" 
bit  in  a  given  spot.  Flat  or  chisel  bits  are  not  recommended 
since  their  reaming  qualities  are  poor,  and  while  cutting  faster 


DRILL  STEEL  AND   DRILL   BITS 


165 


than  the  +  bit  under  some  conditions,  they  are  very  hard  on  the 
machine. 

"It  is  important  to  keep  the  wings  square  at  the  corners,  as 
this  permits  the  gage  of  the  hole  to  be  properly  maintained. 
Do  not  use  a  set  of  steel  after  the  gage  has  begun  to  wear.  The 
time  and  trouble  taken  in  securing  fresh  steel  amount  ta  little 
in  comparison  with  the  delay  caused  by  trying  to  work  down  a 
hole  with  steel  that  is  constantly  sticking,  to  say  nothing  of  the 
wear  and  tear  on  the  machine." 

Mohawk  Bit.  —  A  new  form  of  bit  has  been  in  use  for  some 
time  at  several  mines  in  the  Lake  Superior  copper  region,  espe- 


x\ 


/\ 

/\ 


FIG.  99.  —  The  Mohawk  bit. 


cially  the  Mohawk  and  Wolverine,  and  has  proved  to  be  a  decided 
success.  Two  views  of  this  bit  are  shown  in  Fig.  99.  The  bit 
has  been  named  " Mohawk,"  after  the  mine  in  which  it  was  first 
used.  It  is  employed  in  the  whole  operation  of  drilling,  i.e.,  from 
the  start  to  the  finish  of  a  hole,  although  the  straight-edged  bit 
is  occasionally  employed  as  an  alternate  to  straighten  a  hole. 

The  special  advantage  claimed  for  this  bit  is  that  there  is 
less  danger  of  it  slipping  to  one  side,  and  so  binding  or  becoming 
fitchered,  and  the  projecting  central  portion,  being  driven  on  in 
advance,  acts  as  a  centering  device,  thus  holding  the  body  of  the 
bit  to  its  course.  Aside  from  the  advanced  cutting  edge,  the  bit 
is  simply  the  old  cross  form,  and  has  been  developed  from,  or,  at 
least,  corresponds  to  the  stepped  forms  of  well-drilling  bits  used 


166 


ROCK   DRILLS 


in  Europe.     In  very  hard  ground,  however,  the  advance  cutting 

edge  would  be  smashed. 

Other  Types  of  Drill  Bits.  —  It  will  be  noted  that  in  comparing 
•the  Mohawk  bit,  Fig.  99,  with  Figs.  100,  101, 
and  102,  taken  from  W.  H.  Tinney's  "  Mining 
Machinery,"  the  shoulder  of  the  bit  is  taken  back 
at  right  angles  to  the  cutting  edge,  while  in  the 
other  figures  the  edge  slopes  away  at  an  angle. 
If  the  face  of  shoulder  at  right  angles  to  the 
cutting  edge  is  made  too  long  it  does  not  wear 
down  as  rapidly,  as  the  cutting  edge  of  the  drill 
advances  and  the  drill  will  jamb  in  the  hole. 
If  again,  on  the  other  hand,  the  shoulder  slopes 
away  rapidly  the  bit  loses  its  gage  too  rapidly 
and  the  next  drill  will  not  "  follow."  Fig.  103 
shows  types  of  bits  made  by  the  Word  drill 

FIG.  100.— Star-    sharpener.     Figs.    104    and    105    are    illustrations 
ter,  drillecPor    taken  from  Holman  Brothers'  catalogue.     It  must 
cut  out  1  or  f    be  remembered  that  as 
mch>  the  distance   from    the 


center  of  the  hole  increases  the  amount 
of  rock  to  be  cut  increases  as  the 
square  of  the  radius,  hence  the  out- 
side portions  of  the  cutting  edges  have 
most  to  do.  For  piston  rock  drills  the 
cutting  faces  of  the  chisel  should,  for  FIG. 
hard  ground,  make  an  angle  of  about 

90 


101.    —    Chisel-bit     of 
grooved  steel. 


1 

y\~ 


FIG.  102.  —  Drill  bits. 


with  each  other.  The 
edge  should  be  straight,  not 
convex,  but  if  anything  a  lit- 
tle concave.  The  shoulders 
should  be  well  brought  up 
with  plenty  of  metal  behind 
them,  and  the  gage  should  be 
most  carefully  kept.  E.  K. 
Judd  in  the  Engineering  and 
Mining  Journal,  Dec.  18,  '09, 
discusses  the  question  wheth- 
er drill  bits  should  be  given 
a  concave  or  convex  shape. 


FIG.  103.  —  Types  of  drills  forged  by  the  Ward  drill  sharpening  machine. 


FIGS.  104  and  105.  —  Holman  Brothers  drill  bits. 


168 


ROCK  DRILLS 


He  argues  that  as  the  ends  of  the  bits  have  most  rock  to  exca- 
vate that  the  center  of  the  bit  should  be  advanced  giving  a  convex 
shape.  Chisel  bits,  he  argues,  often  strike  on  a 
corner  owing  to  the  drill  being  not  "true"  in  the 
hole,  which  is  another  reason  they  should  be  given 
a  convex  shape.  The  bit  shown  in  Fig.  101  is 
bad,  as  the  notch  in  center  weakens  the  cutting 
edge  and  the  rounded  shoulders  are  not  an  ad- 
vantage. The  shape  of  the  Anderson  detachable 
bit,  as  shown  in  Fig.  108  and  described,  was  based 
on  a  number  of  experiments  and  is  worthy  of 
study. 

Special  Steel  for  Drilling  Dry  Up-Holes.  —  In 
drilling  dry  holes  at  an  angle  of  less  than  25° 
from  the  horizontal,  difficulty  is  encountered  in 
getting  broken  rock  fragments  away  from  the  face 
and  out  of  the  hole.  A  thin  wire  scraper  is  put 
in  sometimes  and  worked  while  the  bit  is  drilling, 
but  this  does  not  get  the  stuff  away  from  the  face 
of  hole,  consequently  the  bit  does  much  work  twice 
over.  The  Eureka  Drill  Steel  Company  have  in- 
troduced the  steel  shown  in  Fig.  106,  having  lugs 
between  the  ribs  which  pull  out  the  broken  cuttings. 

I  have  recently  introduced  twisted  drill  steel 
(Fig.  107)  to  act  as  a  spiral  conveyor  for  the  same 
purpose.  In  octagonal  steel  a  special  groove  is 
rolled  into  the  steel.  These  devices,  which  are 
patented,  are  simple,  inexpensive,  and  reduce  the 
time  of  boring  flat-holes  or  up-holes  not  steeply 
inclined. 

DETACHABLE  BITS 

The  troubles  incidental  with  moving  the  large 
quantity  of  drill  steel  in  and  out  of  the  mine  to  be 
sharpened,  and  the  losses  in  efficiency  due  to  bits 
having  wings  of  unequal  length,  or  being  bent,  has 
led  to  inventors  seeking  to  perfect  some  form  of 
detachable  bit.  A  bit  is  needed  that  can  be  made 
to  exact  size  and  shape,  which  can  be  attached  to 
a  permanent  shank  and  taken  off  when  blunted.  These  devices 


DRILL  STEEL  AND   DRILL   BITS  169 

have  failed  in  the  past  owing  to  the  difficulty  of  obtaining  a  con- 
nection between  shank  and  head  that  did  not  detach  itself  at  the 
wrong  time  at  the  bottom  of  the  hole.  The  detachable  bits  proved 
expensive  and  were  frequently  left  in  the  ore,  causing  trouble  in 
the  reduction  works.  Major  Derby  had  a  detachable  bit  with  a 


FIG.  107.  —  Twisted  drill  steel  for  removing  broken  rock. 

system  of  water  injection  working  on  the  Hell's  Gate  works,  New 
York,  for  six  months  with  great  success.  The  rock  drill  manu- 
facturers who  bought  the  patent  never  brought  it  before  the  public. 
The  Anderson  Detachable  Drill.  —  The  Anderson  bit  is  shown 
in  Fig.  108.  A  is  the  hollow  shaft  or  shank,  B  is  detachable  bit; 
C  is  front  view  of  bit,  showing  the  hole  for  the  insertion  of  the 
wire,  and  three  cutting  edges,  set  at  angles  of  about  90,  130,  and 


170  ROCK  DRILLS 

140°  with  each  other;  D  is  a  piano  wire  with  f-in.  left-handed 
screw  and  bolt.  The  end  of  the  wire  is  countersunk  in  the  bit; 
G  is  guide  faces,  or  shoulders  cut  in  the  form  of  a  circle;  they  are 
f  in.  deep,  and  have  no  taper  toward  the  back. 

When  using  this  bit  with  the  ordinary  type  of  chuck  in  stand- 
ard machines,  the  chuck  bushing  was  removed  and  a  recess  cut 
back  for  the  projecting  bolt  at  the  end  of  the  shank.  The  shank 
was  thus  supported  by  a  circular  rim.  One  effect  of  increasing 
the  diameter  of  the  shank  was  at  once  noticed.  It  was  much 
more  easily  tightened  up  than  the  ordinary  sized  shank  and  did  not 
work  loose  easily.  Wear  on  the  chuck  was  so  reduced  that  one 
was  used  for  several  weeks  without  sign  of  wear.  For  the  use  of 
this  device  a  special  chuck  would  be  necessary.  When  the  bit 
is  blunted  another  longer  length  is  put  in  machine,  the  rod  un- 
screwed, the  old  bit  taken  off,  and  replaced  by  a  new  one.  Owing 


-2 '-6*- 
A 


according  to  Length 

FIG.  108.  —  Anderson  detachable  bit. 

to  the  central  hole  these  bits  can  be  strung  on  a  string  or  wire  for 
carrying  about.  The  worn  bits  can  be  also  threaded  up,  so  the 
danger  of  them  getting  mixed  with  the  ore  will  be  diminished. 
Mr.  Anderson  states  that  on  the  May  Consolidated,  13  holes  5J 
ft.  deep  were  drilled  in  7  hr.  40  min.,  using  52  bits  or  4  to  a  hole, 
against  5  or  6  with  ordinary  bits.  Regarding  his  bit  as  a  means 
of  increasing  speed  of  drilling,  Mr.  Anderson  states  that  increased 
efficiency  is  due  to  the  following  factors: 

(a)  No  waiting  for  drill  steel. 

(6)  Never  using  a  bit  twice. 

(c)  Drills  always  being  of  standard  lengths. 

(d)  The  gage  or  diameters  being  accurate. 

(e)  All  bits  being  interchangeable  (that  is,  the  starting  bit 
could  be  fixed  to  the  finishing  shank  or  vice  versa). 

({)  The  cutting  edges  being  so  arranged  that  they  always 
form  a  round  hole. 

(g)  The  end  faces  of  the  cutting  edges  form  segments  of  the 
same  circle  and  are  of  such  a  size  that  they  wear  evenly  and 
without  friction. 


DRILL  STEEL  AND   DRILL   BITS  171 

(h)  Ample  clearance  is  allowed. 

(i)  The  permanent  drill  shanks  are  made  much  heavier  than 
the  present  steel,  and  are  capable  of  properly  delivering  the  blow 
without  loss  of  energy  due  to  bending. 

(j)  The  combination  of  an  improved  arrangement  of  cutting 
edges  with  the  increased  strength  of  shank  enable  holes  to  be 
collared  at  angles  which  the  present  steel  cannot  attempt. 

(k)  Due  to  the  precise  gaging  of  the  bits,  holes  can  be  drilled 
starting  with  a  less  diameter  of  bit  and  finishing  larger  than  with 
the  present  steel. 

The  effect  of  the  strong  shank  is  to  deliver  a  heavier  blow,  as 
the  minimum  of  energy  is  lost  in  the  give  of  the  shank.  This 
condition  naturally  causes  more  wear  on  the  cutting  edges.  Mr. 
Anderson  lays  more  importance  on  the  arrangement  of  the  cutting 
edges,  and  especially  on  the  fact  of  the  bit  forming  a  round  hole 
and  having  correct  guiding  faces  which  work  without  friction  in 
that  hole  and  keep  the  bit  concentric  with  the  axis  of  the  piston- 
rod,  than  on  the  degree  of  sharpness  retained  by  the  chisel  edges. 
In  fact,  the  drill  that  has  been  binding  on  the  side  of  the  hole 
keeps  its  edge  better  than  one  which  has  worked  freely. 

He  also  remarks  that  the  usual  form  of  starter  in  practice  was 
2J  in.  to  2f  in.  across  the  cutting  edges,  while  the  side  or  guiding 
faces  of  the  drill  were  about  1J  to  1|  in.,  the  cutting  edges  being 
forged  either  by  hand  or  machine.  These  systems  of  dressing 
the  bit  are  not  accurate,  the  principal  fault  being  that  each  blade 
is  different  in  length.  If  there  is  only  a  difference  of  jV  in.,  one 
guiding  face  is  sure  to  be  out  of  action.  It  is  evident  he  says, 
that  the  bit  or  cutting  head  should  be  exact  to  T&TF  part  of  an 
inch,  and  that  on  striking  the  bottom  of  the  hole  each  edge  should 
carry  its  equal  share  of  the  shock  and  each  guiding  face  its  share 
of  side  pressure.  The  present  drill  steel  is  tapered  down  to  If 
in.  where  attached  to  the  chuck,  and  the  piston-rod,  as  a  rule,  is 
2  in.;  but  he  has  noticed  a  good  many  much  smaller  in  diam- 
eter than  If  in.  The  proportion  between  If  in.  and  If  in.  is 
entirely  wrong  to  transmit  the  heavy  blow  necessary  for  cutting 
hard  rocks.  In  watching  rock  drills  at  work  any  one  with  a 
mechanical  ear  will  suffer  from  the  harsh  sound  which  is  the 
result  of  the  wrong  design  of  drill  steel.  The  continual  jar  and 
shake  due  to  the  want  of  equilibrium  cause  fractures  of  the  piston- 
rod  and  the  drill  steel. 


172 


ROCK   DRILLS 


It  is  left  to  the  care  of  the  blacksmith  to  gage  the  reduction 
in  diameter  of  the  drills,  and  that  is  the  principal  reason  why  they 
start  the  hole  2f  in.  and  finish  up  If  in.  As  the  rate  of  drilling 
is  proportional  to  the  volume  excavated  there  would  be  much 
saving  if  you  could  start  the  hole  with  less  diameter.  With  the 
Anderson  detachable  bit,  the  drill  steel  is  made  If  in.,  where 


FIG.  109.  —  Leyner  patent  starter. 

attached  to  the  chuck.  It  is  hardened  and  tapered  down  to 
the  cutting  head.  There  is  just  enough  guiding  face  on  the  drill 
bit  to  keep  the  whole  true,  and  the  guiding  face  wears  away 
without  any  binding  against  the  side  of  the  hole.  The  bit  is 
never  tight  in  the  hole.  The  guiding  faces  are  also  segments  of 
the  same  circle,  the  bit  being  made  in  dies,  and,  therefore,  being 
perfectly  accurate.  The  bit  is  also  exactly  true  with  the  piston- 


FIG.  110.  —  Correct  drill  bits  (Leyner). 

rod,  and  it  is  impossible  for  the  bit  to  work  out  of  line  without 
pulling  the  piston-rod  with  it.  There  is  no  scoring  in  starting 
a  hole,  and  the  shock  that  is  delivered  through  the  piston-rod  is 
transmitted  to  the  face  of  the  bit  and  is  not  absorbed  in  friction 
on  the  side  faces  or  in  the  loss  of  energy  due  to  want  of  equilib- 
rium on  the  cutting  edges. 

This  bit  is  not  yet  at  work  on  a  large  scale.     Experiments 


DRILL  STEEL  AND   DRILL  BITS 


173 


100 
ob- 


at  several  mines  showed  an  increased  boring  rate  of  from  30  to 

per  cent.     A  certain  amount  of  trouble  was  experienced  in 

taining  bits  of  the  exact  temper  and 

hardness    required,    as    in    the    cases 

noted  of  anvil  blocks  for  hammer  drills. 

Some  bits  blunt  very  rapidly  and  in 

hard  ground  the  shaft,  near  the  bit,  has 

a  tremendous  stress  laid  upon  it  by  the 

rigidity  of  the  shank.     It  is  liable  to 

bend  or  break.     It  is  stated  that  no 

trouble  has  been  occasioned   by  the 

breaking  of  the  piano  wire,  and  that 

no  bits  become  detached. 

The  problem  has  its  financial  side. 
The  weight  of  steel  discarded  is  very 
large  and  it  cannot  often  be  sold  as 
waste  metal  to  advantage.  It  has, 
however,  been  proved  that  there  is 
much  progress  to  be  made  in  correctly 
designing  and  sharpening  bits  for  pis- 
ton drills.  Already  marked  economics 
have  been  shown  by  increasing  the 
diameter  of  the  shanks  of  ordinary 
steels  from  1J  to  1-J-  in.  The  benefits 
to  be  derived  from  accurate  machine 
sharpening  are  here  again  emphasized. 

BITS  FOR  HAMMER  DRILLS 

Leyner  Drill.  —  Figs.  109  and  110 
show  the  bits  recommended  for  Leyner 
drills.  The  shanks  have  lugs  on  them 
for  turning  the  drill. 

Murphy  Drill. —  Fig.  Ill  shows 
bits  used  in  the  Murphy  drill.  A  col- 
lar is  forged  on  the  shank  as  shown  to 
prevent  the  drill  entering  the  cylinder 
of  machine. 

Hardscogg  Drill.  —  Fig.  112  shows 
bits  used  in  the  Hardscogg  Wonder  machine:    (1)  Hexagon  hol- 
low;   (5)  hexagon  solid;    (13)   special  for  soft  rock;    (14)  hexagon 


174 


ROCK  DRILLS 


hollow  8-point;  (15)  special  round  hollow  for  plug  holes.  Bits 
for  all  Wonder  drills  except  No.  18  and  No.  19  are  made  from 
f-in.  hexagon  material,  while  for  the  No.  18  and  No.  19  drills  the 
lengths  up  to  3  ft.  are  made  from  the  1-in.  hexagon  material. 

They  are  all  fitted  with  the  6-point  cutting  surface,  which  in 
ordinary  ground  gives  better  satisfaction  than  any  other  shape. 
There  are  some  cases,  however,  where  the  rock  is  very  soft,  that 
the  8-point  or  the  No.  13  style  bit  will  give  better  service,  but  the 
6-point  is  supplied  in  every  case  where  the  other  shapes  are  not 
specially  ordered. 


No.  1. 


NO.    0. 


No.  13. 


No.  14. 


No.  15. 


FIG.  112.  —  Hardscogg  wonder  drills. 


Waugh  Drill.  —  The  type  of  bit  used  on  this  drill  is  shown 
in  Fig.  113,  and  the  makers  recommend  the  following: 

"Sets  of  steel  ordered  from  us  are  bitted  and  the  shank  ends 
ground  off  smooth  and  hardened.  When  customers  wish  to  make 
up  their  own  steel,  we  desire  to  emphazise  •  the  importance  of 
having  the  shank  ends  ground  off  smooth  and  hardened.  This  will 
present  a  smooth  surface  for  the  tappet  to  strike  against  and  the 
life  of  this  part  will  be  very  materially  prolonged.  The  shank 
ends  should  be  hardened  so  that  they  will  not  upset  or  batter, 
and  stick  in  the  chuck.  They  should  not  be  tempered,  however, 
as  they  will  have  a  tendency  to  sliver  on  the  edges  and  leave  only 
a  small  surface  for  the  tappet  to  strike. 


DRILL   STEEL  AND   DRILL   BITS  175 

''Hexagon  hollow  steel  for  the  drifters  and  sinkers  should 
be  prepared  in  the  same  way  as  the  four-groove  steel  for  the 
stopers,  as  far  as  the  shank  ends  are  concerned.  The  bits  on  hexa- 
gon steel  should  be  4-point,  and  when  forming  the  bit  the  hole 
in  the  center  can  be  allowed  to  come  together,  and  instead  of 
keeping  the  hole  in  the  drill  steel  open  the  entire  length,  a  hole 
should  be  punched  between  two  lips  of  the  bit  about  f  in.  back 
from  the  face,  so  as  to  connect  with  the  hole  in  the  center  of  the 
steel'.  Experience  has  shown  us  that  the  hole  for  the  air  and  water 
to  come  out  will  be  less  likely  to  become  clogged  if  kept  back 
from  the  face  of  the  bit,  and  for  the  purpose  of  keeping  the  cut- 
tings back  from  the  bottom  of  the  hole  will  be  equally  as  efficient." 


FIG.  113.  —  Waugh  drills. 

Latest  Cripple  Creek  Practice.  —  C.  E.  Wolcott  says  that: 
"At  present  there  are  three  main  types  of  bit  used  with  these 
machines  in  the  Cripple  Creek  district.  These  are  illustrated 
in  Nos.  1,  2,  and  3,  Fig.  114.  The  first  is  commonly  called  the 
bull  bit  and  is  made  either  as  illustrated  or  with  the  sides  slightly 
drawn  in  below  the  points  bb  in  the  side  view.  In  either  case  it 
should  be  so  made  that  the  distance  aa  is  greater  than  the  dis- 
tance bb  (plan  view).  The  same  point  should  be  observed  in 
making  the  cross-bit,  No.  2.  By  observing  this  condition  the  edges 
ab  and  be  act  as  reamers  to  cut  away  the  outer  circumference  of 
the  hole.  If  these  edges  become  rounded,  it  becomes  difficult  to 
turn  the  bit  in  the  hole.  This  difficulty  is  overcome,  in  the  third 
style  of  bit  illustrated,  by  rounding  off  the  cutting  edges  as 


176 


ROCK   DRILLS 


shown.  The  degree  of  curvature  may  vary  appreciably,  but  is 
usually  not  very  great.  This  bit  has  been  in  use  a  comparatively 
short  time  but  has  given  great  satisfaction  wherever  used.  This 
bit  not  only  cuts  rapidly  but  it  also  gives  less  trouble  in  turning 
than  either  of  the  others  illustrated,  and  will  cross  slips  more 
readily.  It  is  possible  to  use  this  bit  in  a  hole  that  has  become 
reamed  when  drilling  with  a  square  bit,  and  with  but  little  diffi- 


FIG.  114.  —  Various  shapes  of  bits  used  with  air  hammer  drills. 

culty  to  cut  out  the  reams  and  start  the  drill  to  turning  again. 
This  is  also  true  regarding  a  hole  reamed  by  a  bull  bit." 

Stephens  Drill.  —  The  latest  hammer  drill  manufactured  by 
this   Cornwall   company   employs  tapered   and   collared  shanks, 
with  double  chisel  bits,  shown  in  Fig.  115. 
Sharpening  Machines  for  Hammer  Drills. 
—  Several   manufacturers,  as   Leyner,   Fair- 
banks-Morse,  Hardscogg,   Ingersoll-Sergeant 
Company,  supply  light  sharpening  machines 
worked  by  pneumatic  hammers  for  use  with 
hammer-drill  steel. 

Hollow  Steel.  —  Good  quality  hollow  steel  is  of  recent  manu- 
facture only.  At  first  short  pieces  of  solid  steel  were  bored  out 
and  welded  on  to  iron  tubular  shanks,  but  welds  are  always  a 
source  of  weakness.  The  No.  9  Leyner  still  uses  welded  bits 
owing  to  the  special  shape  of  shank  required.  Hollow  steel  is 


FIG.  115.  —  Stephens 
double  chisel  drill. 


DRILL  STEEL  AND   DRILL  BITS  177 

now  made  by  drawing  out  hollow  billets  and  is  mostly  rolled. 
Most  of  the  hollow  steel  is  of  high  carbon,  0.45  per  cent,  or  over. 
Some  contains  manganese.  It  requires  careful  tempering.  TV  per 
cent  Vanadium  in  steel  has  a  remarkable  effect  in  strengthening 
and  toughening  drill  steel.  Hollow  steel  can  be  welded  to  pre- 
serve the  central  hollow  core  by  greatly  enlarging  the  core-before 
the  weld  is  hammered. 


EXPLOSIVES  AND   THEIR  USE 

THIS  is  not  a  handbook  of  explosives  so  I  shall  give  only  a 
few  particulars  regarding  the  types  of  powder  in  most  common 
use  in  mining,  with  notes  on  their  employment  and  on  the  theory 
of  blasting.  The  chief  explosives  in  use  in  metalliferous  mines 
are  (1)  Low  explosives,  as  ordinary  gunpowder  and  compressed 
gunpowder;  (2)  High  explosives,  as  dynamite,  gelignite,  gelatine 
dynamite,  blasting  gelatine,  tonite  or  cotton  powder,  Atlas  pow- 
der, Hercules  powder,  giant  powder,  forcite,  rack  a  rock,  Judson 
powder  and  jovite. 

Gunpowder.  —  The  composition  varies  from  65  to  75  per  cent, 
niter,  10  to  15  per  cent,  sulphur,  and  15  to  20  per  cent,  charcoal. 
It  is  sometimes  used  in  very  soft  or  loose  ground,  where  a  heaving 
or  rending  effect  is  required  and  where  the  rock  is  so  full  of  cracks 
that  the  gases  of  a  high  explosive,  being  more  rapidly  evolved, 
would  escape  before  doing  their  work.  It  is  sometimes  used  in 
large  blasts,  mixed  with  high  explosives  for  the  same  reason. 

HIGH  EXPLOSIVES 

Dynamite.  —  A  mixture  of  various  proportions  of  nitroglycer- 
ine with  some  porous  and  more  or  less  inert  substance  that  will 
absorb  the  liquid.  Keiselguhr  or  infusorial  earth  was  first  em- 
ployed by  Nobel,  the  inventor.  Most  of  the  powders  used  in 
America  are  dynamites  with  a  low  percentage  of  nitroglycerine, 
having  absorbents  calculated  to  increase  the  force  of  the  explosion 
of  the  powder.  In  America  40  per  cent,  dynamite  is  commonly 
used  in  mining  fairly  hard  ground.  It  consists  of  40  per  cent, 
nitroglycerine,  47.25  per  cent,  sodium  nitrate,  11.75  per  cent, 
wood  pulp,  and  1  per  cent,  calcium  carbonate.  The  composition 
of  these  explosives  is  given  because  the  rock  driller,  to  use  them 
safely  and  economically,  must  know  something  of  their  con- 
stituents and  properties. 

Gelignite.  —  This  consists  of  nitroglycerine  and  nitrocellulose 

178 


EXPLOSIVES  AND  THEIR  USE  179 

with  a  certain  proportion  of  nitrate  of  potash  and  wood  meal. 
It  is  more  plastic  than  dynamite  and  12  per  cent,  more  powerful. 

Gelatine  Dynamite.  —  This  explosive  consists  of  80  per  cent, 
nitrocellulose  or  blasting  gelatine,  with  a  certain  proportion  of 
nitrate  of  potash.  It  is  considered  25  per  cent,  stronger  than 
No.  1  dynamite. 

Blasting  Gelatine.  —  It  is  composed  of  93  per  cent,  nitroglycer- 
ine, solidified  by  means  of  collodion.  It  is  a  solid  plastic  jelly. 
It  is  the  explosive  par-excellence  for  mining  work  in  the  hardest 
and  strongest  rocks.  It  explodes  if  heated  to  400°  F.  It  freezes 
at  35°  to  40°  F.,  and  is  very  sensitive  to  shock  when  frozen.  Water 
is  not  absorbed,  nor  does  it  leak  nitroglycerine;  hence  can  be 
used  safely  under  water. 

For  cite.  —  This  is  really  a  thin  blasting  gelatine  mixed  with 
nitrate  of  soda,  and  coated  with  molten  sulphur  and  wood  tar. 
It  contains  1  per  cent,  wood  pulp.  Nitroglycerine  will  leak  out. 

Atlas  Powder.  —  The  composition  is,  nitroglycerine  75  per 
cent.,  wood  fiber  21  per  cent.,  nitrate  of  soda  2  per  cent.,  and 
2  to  3  per  cent,  carbonate  of  manganese.  It  is  made  in  grades 
containing  from  20  to  75  per  cent  nitroglycerine. 

Hercules  Powder.  —  The  highest  grade  contains  75  per  cent, 
nitroglycerine,  20  per  cent  carbonate  of  manganese,  2.1  per  cent, 
nitrate  of  soda,  1.05  per  cent,  chlorate  of  potash,  and  1  per 
cent,  white  sugar.  The  carbonate  of  manganese  is  the  absorbent. 

Judson  Powder.  —  The  composition  varies  in  some  cases  5 
to  15  per  cent.  Nitroglycerine  is  added  to  a  mixture  of  15  parts 
sulphur,  3  parts  resin,  2  parts  asphalt,  70  parts  nitrate  of  soda, 
10  parts  anthracite  coal.  In  all  these  explosives  nitroglycerine 
is  the  important  constituent. 

Tonite.  —  This  is  a  nitrated  guncotton.  Barium  nitrate  is 
generally  used.  Tonite  is  not  plastic  and  is  of  equal  strength  to 
dynamite  No.  1.  It  contains  no  nitroglycerine. 

Rack-a-Rock.  —  It  consists  of  79  parts  chlorate  of  potash  and 
21  parts  of  mono-nitrobenzine,  which  are  mixed  just  before  use. 
Nitroglycerine  is  not  a  constituent  in  this  powder. 

Nitroglycerine.  —  This  is  a  very  high  power  explosive  made 
by  the  action  of  concentrated  nitric  acid  on  glycerine.  It  is  a 
clear  oily  liquid  with  a  specific  gravity  of  1.6.  When  applied  to 
the  skin  it  produces  headache  and  sickness;  some  people  being 
more  susceptible  than  others.  Hence  dynamite  and  like  explosives 


180  ROCK   DRILLS 

should  not  be  handled  too  much  with  bare  fingers.  Over  10 
grains  acts  as  a  fatal  poison  if  swallowed.  It  may  be  heated  to 
100°  C.  without  explosion,  but  is  then  very  sensitive  to  shock. 
At  257°  C.  it  detonates.  One  volume  of  nitroglycerine  produces 
1200  to  1500  volumes  of  gas,  which  is  expanded  eight  times  by 
the  heat  of  combustion.  A  sudden  blow  will  evolve  enough  heat 
to  detonate  it;  but  only  that  portion  struck.  If  frozen,  however, 
the  detonation  is  distributed  over  all  the  mass.  The  direct  rays 
of  the  sun  decompose  nitroglycerine  into  an  unstable,  easily 
exploded  substance.  The  burning  of  nitroglycerine  or  its  incom- 
plete detonation  set  free  gases  that  are  poisonous  to  the  human 
system.  The  most  important  of  these  are  carbon  monoxide  and 
nitrous  acid.  The  gases  produce  symptoms  and  effects  known 
among  miners  as  "gasing."  American  miners  call  blasts  that 
produce  a  large  proportion  of  such  gases,  'stinkers.'1  Nitro- 
glycerine will,  under  water,  exude  from  dynamites,  but  not  from 
blasting  gelatine. 

Many  of  the  various  nitrates  are  deliquescent;  i.e.,  absorb 
moisture  from  the  air  and  are  soluble  in  water.  Explosives  con- 
taining these  should  be  stored  in  dry  places  and  not  used  if  they 
show  on  the  surface  a  frosted  appearance,  which  shows  that  this 
action  has  begun.  Nitroglycerine  and  the  explosives  containing 
it  freezes  at  42°  to  46°  F.  When  frozen,  dynamite  cannot  be 
exploded  by  the  ordinary  detonators.  Blasting  gelatine  is  not 
properly  detonated  while  frozen. 

Thawing  Explosives.  —  Numerous  accidents  occur  through 
doing  this  improperly.  Nitroglycerine,  especially  in  the  higher 
grades  of  dynamite,  tends  to  exude  from  its  "dope,"  or  absolvent, 
when  subject  to  heat  in  the  presence  of  water.  Frozen  dynamite 
and  blasting  gelatine  are  also  sensitive  to  friction.  Cutting  or 
breaking  a  cartridge  while  frozen  is  dangerous.  On  the  other 
hand,  should  nitroglycerine  exude  under  heat  it  is  most  sensitive 
to  shock  and  even  a  drop  falling  will  often  explode.  Leaking 
dynamite  is  shown  by  the  oily  appearance  of  the  wrapper,  or  by 
drops  forming.  If  the  wrapper  is  discolored  by  greenish  stains 
it  shows  that  the  nitroglycerine  has  begun  to  decompose  and  it 
should  be  at  once  destroyed.  Frosted  dynamite  will  almost  cer- 
tainly leak  and  should  be  carefully  removed  and  destroyed  by 
burning  in  a  safe  place.  It  is  best  to  lay  the  sticks  touching  one 
another  in  a  row  and  light  the  end  one.  Since  both  cold  and  hot 


EXPLOSIVES   AND   THEIR  USE 


181 


water  tend  to  displace  the  nitroglycerine  in  dynamite,  cartridges 
should  never  be  softened  by  the  use  of  steam  or  hot  water.  Nor 
should  they  be  subjected  to  a  dry  heat  that  can  possibly  rise 
above  212°  F.  For  this  reason,  thawing  by  placing  near  a  fire, 
boiler,  stove,  or  other  such  place  is  unsafe.  Dynamite  may  be 
thawed  by  being  placed  in  a  room  or  box  heated  by  hot  water  pipes. 
Small  amounts  might  be  thawed  by  being  placed  in  a  room  or 
box  with  a  can  of  hot  water  placed  in  with  them  at  a  safe  distance. 
The  safest  way  of  thawing  is,  perhaps,  to  place  a  box,  containing 
the  dynamite,  in  the  center  of  a  heap  of  green  manure,  where  an 


FIG.  116.  —  Dynamite  stone  house. 

even  heat  is  maintained.  Since  the  contraction  and  expansion  of 
freezing  and  thawing  itself  tends  to  displace  nitroglycerine  all 
cartridges  thawed  should  be  examined  before  use.  Where  elec- 
tric power  is  available,  suitable  thawing  boxes  heated  by  the  elec- 
tric current  and  having  the  heat  under  complete  control  can  be 
easily  constructed  by  any  electrician.  Dynamite  is  sold  in  sticks 
or  cartridges.  A  No.  1  dynamite  stick  is  1}  in.  in  diameter. 
8  in.  long,  and  weighs^0.5  to  0.6  Ib. 

Dynamite  Storehouse.  —  In  a  recent  bulletin  of  the  Societe  de 
PIndustrie  Minerale,  Gaston  Beuret  describes  a  rather  elaborate 
structure,  Fig.  116,  for  the  storage  of  explosives  that  was  built 
in  connection  with  shaft  development  at  Sancy.  Its  design  was 


182  ROCK   DRILLS 

fully  approved  by  the  administration  of  mines.  It  is  150  m.  from 
the  nearest  building. 

The  chamber  was  built  of  the  best  ashlar  masonry,  after  the 
plan  shown  in  the  accompanying  drawing,  and  was  then  covered 
at  least  4  m.  deep  with  screened  earth,  with  all  the  small  stones  re- 
moved. Opposite  the  entrance  was  built  a  smaller  pile  of  earth  with 
a  masonry  niche  designed  to  catch  and  render  harmless  any  ma- 
terials thrown  out  of  the  entrance  passage  in  case  of  an  explosion. 

A  chimney  extends  from  the  level  of  the  chamber  floor  to  a 
height  of  2  m.  above  the  top  of  the  dirt  pile.  The  flue  connecting 
the  interior  of  the  chamber  with  this  chimney  slopes  downward 
so  as  to  prevent  the  admission  of  any  burning  or  inflammable 
substance  into  the  chamber.  The  top  of  the  chimney  is  further 
protected  by  a  grating. 

The  outer  entrance  is  closed  by  a  firmly  locked  iron  door,  and 
the  inner  entrance  to  the  storage  chamber  is  closed  by  a  locked 
wooden  door.  A  barbed  wire  and  picket  fence  surrounds  the 
magazine  at  a  distance  of  50  m.  The  doors  are  connected  elec- 
trically with  an  alarm  in  the  mine  office,  in  such  manner  that  the 
opening  of  either  door,  or  the  cutting  of  the  electric  wire,  will 
give  a  signal.  The  storage  chamber  was  designed  to  hold  200  kg. 
of  dynamite,  which  obviated  too  frequent  handling  in  the  winter. 

The  Transvaal  government  has  issued  strict  regulations 
dealing  with  the  storage  of  explosives. 

BLASTING 

Charging  with  Gunpowder.  —  The  hole  must  be  properly  dried 
by  inserting  a  rod  having  cotton  waste,  cloth,  straw,  etc.,  fastened 
to  one  end.  In  small  holes  a  long  tin  funnel  is  employed  for 
charging.  The  stem  is  inserted  nearly  to  the  bottom  of  the  hole, 
thus  there  is  no  chance  of  any  of  the  powder  sticking  to  the  sides. 
With  flat  holes,  or  "up"  holes  the  powder  is  best  made  up  into 
paper  cartridges.  The  experiments  of  Sir  J.  F.  Burgoyne  have 
shown  that  in  holes  of  one  inch  diameter,  7  in.  of  clay  tamping 
are  sufficient;  holes  2  in.  in  diameter,  18  in.,  and  in  holes  3  in.  in 
diameter,  20  in.  Generally,  it  may  be  said  that  tamping  is  most 
important;  the  better  it  is  done  the  better  will  the  results  be. 
The  charge  should  fill  the  chamber  or  hole;  there  should  be  no 
space  left  between  it  and  the  tamping  as  the  presence  of  any  air 
acts  as  a  cushion  to  the  force  of  the  blast. 


EXPLOSIVES  AND  THEIR  USE  183 

Ignition  of  a  Powder  Charge.  —  This  is  now  performed  by 
means  of  safety  fuse  which  consists  of  a  core  of  special  gunpowder 
surrounded  by  tape  or  tape  and  gutta-percha.  One  end  is  inserted 
in  the  powder  before  placing  the  tamping  in  the  hole.  The  rate 
of  burning  of  this  fuse  per  yard  is  known  and  a  sufficient  length 
cut  to  allow  ample  time  for  the  operator  to  retire  in  safety.  _ 

Where  numerous  holes  are  fired  simultaneously  low-power 
electric  exploders  are  employed. 

DETONATION  OF  HIGH  EXPLOSIVES 

The  difference  between  this  operation  and  that  of  firing  low 
explosives  is  that  the  first  are  exploded  by  simple  ignition.  Explo- 
sives containing  nitroglycerine  can  be  thoroughly  exploded  only 
by  detonation.  The  following  extracts  from  a  paper  by  Roland 
L.  Oliver  present  the  facts  regarding  high  explosives,  their  detona- 
tion, and  the  precautions  to  be  observed  in  their  use  in  a  practical 
manner.  It  is  easily  understood  by  any  one,  so  I  reproduce  them. 

Maximum  Strength  of  Powder  —  How  Produced.  —  Detonators 
or  blasting  caps  are  made  in  several  different  grades  of  strength, 
because  some  powders  require  not  only  a  greater  but  a  different 
initial  detonation  than  others  to  convey  their  maximum  energy 
through  a  whole  charge,  and  the  detonating  qualities  of  each 
powder  vary  by  changes  in  its  physical  condition  —  whether  it 
be  warm  or  cold,  rigid,  plastic,  homogeneous  or  otherwise. 

The  full  significance  of  "detonation,"  as  applied  to  high  explo- 
sives, will  become  apparent  in  the  course  of  this  paper,  but  briefly 
it  may  be  stated  that  detonation  is  a  very  much  higher  degree 
of  explosion  than  that  produced  by  fire  alone  or  by  a  blow.  While 
either  of  these  will  explode  powder  under  certain  conditions, 
neither  of  them  will  cause  it  to  produce  its  greatest  effect.  An 
explosion  is  merely  the  rapid  transformation  of  powder  from  its 
solid  or  liquid  state  into  gases  which  struggle  to  occupy  a  space 
hundreds  of  times  greater  than  that  occupied  by  the  original 
substance;  but  in  order  that  these  gases  may  produce  their  greatest 
rupturing  force  on  the  surrounding  material,  they,  too,  must 
be  expanded  suddenly  to  their  greatest  possible  volume.  This 
requires  a  practically  instantaneous  decomposition  and  oxidation 
at  maximum  temperature  into  their  simplest  elements,  the  result 
being  the  highest  degree  of  explosion,  which  is  called  "  detonation," 
and  which  can  only  be  produced  by  a  peculiar  combination  of 


184  ROCK  DRILLS 

intense  heat  and  concussion,  such  as  is  supplied  through  the  agency 
of  detonators,  or  blasting  caps,  as  they  are  commonly  called. 
Hence,  a  thorough  detonation  of  powder  is  controlled  by  the 
cap,  the  nature  and  strength  of  which  is  as  essential  to  successful 
results  as  is  the  powder  itself. 

The  susceptibility  of  powder  to  detonation  depends  more 
upon  the  nature  of  its  ingredients  and  on  the  physical  conditions 
previously  mentioned  than  on  the  amount  of  nitroglycerine  or 
high  explosive  which  it  may  contain.  For  instance,  ordinary 
dynamite,  with  40  per  cent,  nitroglycerine,  is  easier  to  detonate 
thoroughly  than  a  gelatine  dynamite  containing  even  as  much  as 
80  per  cent,  nitroglycerine,  because  in  the  first  the  liquid  nitro- 
glycerine is  merely  absorbed  mechanically  in  a  dope,  whereas  in 
the  latter  it  is  chemically  transformed  with  guncotton  into  a 
gelatinized  mass,  which  is  harder  to  detonate  and  harder  to  make 
transmit  its  detonation  through  a  whole  charge  of  it  than  ordinary 
dynamite;  that  is,  a  comparatively  weak  cap  will  detonate  a  larger 
charge  of  straight  dynamite  than  of  gelatine  dynamite,  yet  gela- 
tine dynamite,  when  detonated  with  a  suitable  cap,  is  somewhat 
stronger  than  ordinary  dynamite  containing  the  same  amount 
of  nitroglycerine  and  possesses  greater  shattering  effect. 

A  spark  will  detonate  fulminate  of  mercury;  2  grains  of  ful- 
minate will  detonate  nitroglycerine;  but  it  requires  at  least  10 
grains  of  fulminate  to  detonate  guncotton.  That  there  is  some- 
thing more,  however,  than  the  actual  force  and  quickness  of  these 
10  grains  of  fulminate  is  shown  by  the  fact  that,  although  the 
mechanical  force  of  nitroglycerine  is  more  than  that  of  fulminate 
of  mercury,  or  ten  times  more  than  nitroglycerine,  100  grains,  will 
not  detonate  guncotton;  it  will  only  scatter  it,  yet  a  small  quantity 
of  dry  guncotton,  which  is  slower  than  nitroglycerine,  will  easily 
detonate  nitroglycerine  and  even  wet  guncotton,  which  are  the 
two  extremes,  nitroglycerine  being  one  of  the  most  sensitive  and 
wet  guncotton  one  of  the  most  inert  forms  of  high  explosives. 
Therefore  the  equilibrium  of  the  different  chemical  molecules  of 
these  powders  is  susceptible  to  explosion  not  merely  by  the  force 
of  the  shock,  but  by  different  kinds  of  impulses  or  vibrations. 
Another  example  of  the  disruptive  effect  of  a  particular  wave 
motion  without  especial  mechanical  force  are  the  glass  globes, 
frequently  exhibited  in  physical  laboratories,  which  withstand  a 
strong  blow,  but  are  shattered  by  the  mere  vibration  of  a  par- 


EXPLOSIVES  AND   THEIR  USE  185 

ticular  musical  note,  whereas  a  note  of  different  tone  will  not 
affect  them. 

The  different  degrees  of  facility  with  which  some  explosives 
will  detonate  others,  and  their  susceptibility  to  one  kind  of  detona- 
tion more  than  to  another,  must  now  be  apparent.  Let  us  next 
consider  the  action  of  the  same  explosive  under  different  influences. 
It  appears  to  many  that  when  a  charge  of  powder  explodes  at  all, 
it  explodes  with  maximum  force  throughout,  but  such  is  not  the 
case.  For  instance,  a  large  number  of  sticks  suspended  in  the 
air  close  enough  to  explode  one  another  (12  to  36  in.  apart,  accord- 
ing to  the  kind  of  powder  and  size  of  cartridges  used)  will  explode 
down  the  line  for  a  certain  distance  if  a  detonator  be  used  to 
start  the  first  stick,  but  a  point  will  eventually  be  reached  where 
one  will  not  set  off  the  stick  next  to  it,  showing  conclusively  that 
each  successive  stick  of  powder  has  lost  some  of  its  detonating 
force. 

That  its  explosive  force  also  becomes  weakened  as  it  proceeds 
down  the  line  may  be  illustrated  by  placing  under  each  stick  a 
thin  plate  of  soft  steel  over  the  end  of  a  piece  of  4-  or  6-in.  iron 
pipe.  The  force  of  each  explosion  striking  these  plates  of  steel 
will  cup  them  into  the  hollow  of  the  pipe  and  the  size  of  the  cups 
will  diminish  as  the  explosion  gets  farther  away  from  the  initial 
detonation.  It  has  also  been  demonstrated  that  when  the  first 
stick  is  fired  with  a  weak  cap  the  sympathetic  detonation  will 
not  extend  far  down  the  line;  per  contra,  a  very  strong  cap,  or 
one  of  some  other  composition  to  which  the  powder  is  more 
susceptible,  will  carry  the  detonation  much  farther. 

Difference  between  Combustion,  Explosion,  and  Detonation.  — 
The  effect  of  merely  lighting  a  piece  of  unconfined  dynamite  with 
a  squib  or  piece  of  fuse  without  any  cap  attached  is  that  the  dyna- 
mite will  burn  quickly  without  exploding,  and  make  a  dense  smoke 
which  has  a  disagreeable  smell  and  produces  violent  headaches 
and  if  breathed  in  large  quantities  prdduce  death.  This  is 
simple  combustion.  Confine  another  piece  of  dynamite,  and 
light  it  in  the  same  way  and  it  will  explode,  but  it  will  belch 
forth  similar  fumes.  A  very  weak  cap,  like  the  old  single-force 
cap,  fired  in  dynamite  will  explode  it  with  considerable  energy, 
but  there  will  still  be  some  of  the  objectionable  smoke.  Repeat 
the  experiment  with  a  triple-force  cap  and  the  dynamite  will  be 
detonated  with  great  violence  even  when  unconfined,  developing 


186  ROCK  DRILLS 

great  explosive  force  and  very  little  smoke.  This  illustrates  the 
difference  between  combustion,  explosion,  and  detonation,  show- 
ing that  the  same  powder  may  be  made  to  transmit  its  energy 
by  different  means  and  with  different  degrees  of  intensity  from 
a  rapid  burning  to  a  violent  detonation. 

The  relative  strengths  of  three  well-known  explosive  com- 
pounds have  been  compared  when  exploded  by  fire  simply  and 
then  by  detonation.  Considering  the  explosion  from  simple 
inflammation  of  gunpowder  as  unity,  guncotton  when  exploded 
simply  by  fire  is  three  times  stronger  than  gunpowder,  and  when 
detonated  by  a  cap  it  is  six  and  one  half-times  stronger.  Nitro- 
glycerine is  five  times  stronger  than  gunpowder  when  exploded 
by  fire  and  ten  times  stronger  when  detonated.  Hence,  these 
figures  explain  the  enormous  force  which  is  given  by  detonation 
as  compared  with  that  by  simple  explosion. 

Conditions  Influencing  Different  Powders.  —  Gelatine  powders 
do  not  transmit  their  explosive  energy  through  themselves  as 
readily  or  as  far  as  regular  dynamites,  hence  they  require  a  stronger 
detonator,  larger  cartridges  and  more  confinement  to  completely 
detonate  a  whole  charge.  A  3X  cap  gets  nearly  all  the  energy 
out  of  No.  1  and  No.  2  dynamite,  but  gelatine  dynamites,  nitro- 
gelatine  and  other  inert  powders  require  at  least  a  5X  cap  to 
develop  their  energy,  and  a  6X  or  stronger  cap  will  do  it  still 
better,  especially  if  the  charge  be  a  long  one.  This  relation 
between  the  length  of  charge,  the  diameter  of  the  stick,  and  the 
strength  of  caps  is  another  noteworthy  fact,  more  marked  with 
the  inert  powders  than  with  ordinary  dynamite.  Thin  sticks 
require  a  stronger  cap  than  sticks  of  larger  diameter,  and  a  long 
charge,  especially  of  slender  sticks,  requires  a  stronger  cap  to 
convey  sufficient  impulse  through  the  whole  charge;  otherwise 
all  the  powder  in  the  hole  will  not  be  detonated. 

The  so-called  "fumeless  powders,"  meaning  that  their  gases 
are  not  visible  or  noxious,  are  only  fumeless  in  that  sense  of  the 
word  when  well  detonated.  If  the  fuse  burns  them,  or  the  cap 
is  too  weak,  they,  too,  make  " stinkers"  and  produce  headaches. 
A  poor  detonation  of  gelatine  and  other  inert  powders,  which 
does  not  go  all  through  the  charge,  will  disintegrate  some  of  the 
other  sticks  without  exploding  them,  leaving  the  hole  unbot- 
tomed  and  scattering  the  unexploded  powder  about  the  mine, 
which  is  dangerous.  This  sometimes  happens  when  the  cap  has 


EXPLOSIVES  AND  THEIR  USE  187 

been  buried  under  several  sticks  of  powder  and  there  is  no  tamp- 
ing on  top  of  the  charge. 

The  matter  of  tamping  high  explosives  is  much  debated 
amongst  miners,  many  asserting  that  it  is  unnecessary.  As  a 
matter  of  fact,  tamping  is  not  so  essential  with  high  explosives 
as  with  black  blasting  powder,  because  in  the  one  case  the  expan- 
sion of  gases  is  so  sudden  that  just  a  small  proportion  gets  a  chance 
to  escape,  while  in  the  case  of  slower  powders  the  expansion  is 
gradual;  but  in  any  explosive  the  better  the  confinement  of  the 
gases  the  greater  will  the  effect  be.  The  fact  is,  however,  that 
most  blasters  use  an  excess  of  powder  so  as  to  make  doubly  sure 
of  breaking  the  ground,  and  this  excess  also  makes  up  for  the 
loss  of  power  by  the  escape  of  untamped  gases. 

Close  confinement,  by  ramming  the  powder  well  into  a  hole 
so  as  to  fill  up  any  spaces  around  the  charge,  is  also  important, 
as  much  of  its  effectiveness  may  otherwise  be  lost.  For  example, 
a  quarter  of  an  ounce  of  No.  2  dynamite  will  throw  a  ball  of  cer- 
tain weight  from  a  mortar  300  ft.  Leave  f-in.  air  space  between 
the  ball  and  the  powder  and  the  same  quantity  of  dynamite  will 
throw  the  same  ball  only  210  ft.,  lessening  the  distance  90  ft.  in 
300,  which  is  a  loss  of  30  per  cent,  of  its  efficiency. 

Several  years  ago  a  mining  superintendent  in  Arizona  noticed 
irregularities  in  the  progress  of  different  shifts.  Some  of  the 
miners  complained  of  unbottomed  holes  and  bad  air.  He  was 
supplying  them  with  40-per  cent,  gelatine  dynamite,  |-in.  sticks 
and  5X  caps,  shift  and  shift  alike,  but  with  no  more  powder  than 
his  foreman  considered  was  sufficient  to  do  the  work.  Upon  inves- 
tigation it  was  found  that  one  shift  always  rammed  the  charges 
with  a  wooden  bar  and  put  tamping  on  top,  but  the  other  shift  was 
not  tamping.  All  hands  have  been  using  tamping  ever  since,  and 
work  has  proceeded  satisfactorily  with  the  same  powder  and  caps. 

Another  consideration  in  handling  any  powder  is  the  diameter 
of  the  sticks  used.  Seven-eighths-inch  sticks  require  more  con- 
finement and  greater  initial  impulse  than  IJ-in.  sticks  to  carry 
the  detonation  through  the  charge,  because  the  more  powder 
there  is  in  the  immediate  vicinity  of  the  cap,  the  .greater  will  be 
the  initial  explosive  energy  established,  and  this  is  particularly 
essential  with  gelatine  dynamites  and  other  inert  powders. 

When  powder  becomes  chilled,  it  is  difficult  to  detonate  it 
properly  with  the  usual  detonator,  hence  the  advisability  of  using 


188  ROCK  DRILLS 

a  very  strong  cap  in  cold  weather.  Many  of  the  holes  are  fre- 
quently loaded  for  some  time  before  firing,  and  even  if  the  powder 
is  soft  and  normal  while  charging,  it  afterward  becomes  somewhat 
chilled  in  the  cold  ground.  As  said  before,  a  3X  cap,  or  even  a 
double-force  cap,  will  detonate  ordinary  dynamite  if  it  be  soft 
and  plastic.  But  on  the  other  hand,  if  it  be  hard,  or  if  it  should 
present  a  mottled  appearance,  even  a  5X  cap  may  fail  to  detonate 
it  completely. 

Selection  of  Detonators.  —  It  is  the  nature  of  the  initial  detona- 
tion of  the  powder  around  the  cap  which  governs  the  greater  or 
less  effect  of  the  explosion  of  the  whole  charge.  The  cap  com- 
municates to  the  first  particles  of  powder  a  disruptive  impulse, 
which  according  to  the  nature  and  strength  of  the  cap  more  or 
less  completely  overthrows  their  equilibrium  and  decomposes  the 
powder  with  great  energy,  setting  up  sympathetic  vibrations 
which  explode  the  next  particles  of  powder  and  so  on  by  the  violent 
disturbances  or  friction  between  them  in  a  regular  succession  of 
impulses  and  decompositions,  which,  if  started  with  sufficient 
energy,  are  of  such  intense  heat  and  velocity  that  the  rupturing 
force  of  the  explosive  is  developed  practically  instantaneously. 
This  detonation  has  already  been  shown  to  be  not  only  the  result 
of  mechanical  force,  but  a  combination  of  extremely  sudden 
chemical  and  dynamical  or  impulsive  reactions  which  set  up 
vibrations  to  which  different  powders  are  more  or  less  susceptible. 
These  explosive  reactions  will  be  propagated  through  the  mass 
of  the  powder  according  to  the  intensity  of  the  vibrations  and 
the  resistance  with  which  their  motion  is  opposed  by  the  nature 
and  consistency  of  the  powder,  whether  it  be  difficult  or  easy  to 
oxidize,  soft  and  plastic  like  dynamite,  or  hard.  If  the  initial 
detonation  of  the  powder  surrounding  the  cap  is  of  the  highest 
degree,  the  vibrations  will  be  most  intense  and  will  be  propa- 
gated farther  through  the  mass  than  by  a  poorer  detonation. 
Hence  the  different  degrees  of  detonation.  Unless  the  first  par- 
ticles of  powder  are  so  thoroughly  decomposed  by  a  detonation 
of  high  order,  or  first  degree,  as  to  convey  the  necessary  heat  and 
energy  to  detenate  the  whole  charge,  the  greatest  force  of  the 
powder  will  not  be  developed.  There  will  frequently  be  unbot- 
tomed  holes  or  pieces  of  unexploded  powder  scattered  about,  or 
both,  and  the  air  in  the  mine  will  be  contaminated  with  some 
obnoxious  gases  which  have  not  been  completely  oxidized. 


EXPLOSIVES  AND   THEIR  USE 


189 


The  accompanying  illustrations  are  from  cross-sections  of 
explosions  in  solid  lead  cylinders,  and  represent  graphically  the 
difference  in  force  developed.  Fig.  117  is  a  good  detonation  from 
a  strong  cap.  Fig.  118  is  a  poor  detonation  from  a  weak  cap  in 
the  same  quantity  of  powder.  Some  powders  may  lose  as  much 
as  20  per  cent,  of  their  effectiveness,  unless  fired  with  a  suitable 
cap.  No.  1  dynamite  poorly  detonated  is  less  effective  and  more 
obnoxious  than  No.  2  dynamite  thoroughly  well  detonated. 

A  good  rule  is  to  use  a  cap  of  a  grade  too  strong  rather  than 


FIGS.  117  and  118.  —  Results  obtained  from  use  of 
strong  and  weak  detonators. 

too  weak.  The  strongest  cap  is  always  best  adapted  to  the  longest 
hole,  and  is  therefore  the  most  economical. 

It  is  customary  to  speak  of  caps  as  being  of  different  degrees 
of  strength.  This  is  correct,  but  it  means  more  than  the  mere 
mechanical  force  attained  by  different  quantities  of  any  particular 
detonating  substance.  It  is  the  power  or  ability  of  that  deto- 
nating substance  by  its  peculiar  dynamical  and  chemical  nature 
to  transform  instantly  an  explosive  into  a  state  of  great  energy, 
and  it  has  been  shown  in  'the  early  part  of  this  paper  that  equal 
parts  of  some  detonating  substances  possess  this  power  immensely 
more  than  others. 

Different  brands  of  blasting  caps  contain  different  detonating 
mixtures,  but  they  are  supposed  to  be  numbered  or  graded  accord- 


190  ROCK  DRILLS 

ing  to  their  detonating  power,  regardless  of  the  weight  of  explosive 
which  they  contain.  It  was  the  custom  in  early  days  of  dynamite 
to  grade  caps  according  to  the  weight  of  straight  fulminate  of 
mercury  which  they  contained,  because  Nobel,  the  discoverer, 
found  that  a  gun  or  rifle  cap,  which  contained  only  half  a  grain 
of  fulminate,  would  partially  explode  straight  nitroglycerine,  and 
that  its  explosive  force  was  increased  in  proportion  to  the  increased 
weight  of  fulminate  up  to  5  grains,  which  seemed  to  get  the  maxi- 
mum energy  out  of  this  particular  explosive.  But  other  explo- 
sives required  still  more  fulminate,  some  up  to  30  grains  or  more, 
according  to  the  length  of  charge  to  be  detonated.  Whenever 
fulminate  of  mercury  is  used,  it  must  be  incorporated  with  other 
ingredients  to  make  the  cap  safe  to  handle.  Some  of  these  ingre- 
dients lessen  its  detonating  effect,  others  intensify  it,  so  the  effects 
from  given  weights  of  fulminate  have  always  been  referred  to  as 
standards  for  different  grades. 

It  is  well  to  emphasize  the  fact  that  as  their  cost  is  small 
compared  with  the  cost  of  drilling  and  preparing  holes,  none  but 
the  very  strongest  and  best  detonators  should  be  employed. 
Consider  first  the  powder  and  conditions  under  which  it  is  to  be 
used,  then  select  a  detonator  which  will  develop  the  greatest 
energy  out  of  that  particular  powder  under  those  conditions. 
Properly  made  detonators,  if  not  tampered  with,  should  be  safe 
to  handle  regardless  of  their  strength. 

Electrical  fuses  or  exploders  are  for  firing  blasts  by  electricity. 
Electrical  fuses  are  built  into  the  blasting  caps  and  form  a  part 

of  them,  Fig.  119.  They  are 

sealed  up  air  tight,  and  are  as 
FIG.  119.  —  Electric  fuse.  ,  e  u  ,,  . 

nearly  waterproof  as  such  things 

can  be  made  without  expensive  rubber  insulation;  but  when 
handled  with  ordinary  care  may  be  used  freely  under  water, 
except  when  very  deep,  in  which  case  they  require  special  insu- 
lation and  reinforced  cartridges. 

Misfires  and  how  to  Avoid  Them.  —  No-blasting  cap,  unless  it 
be  a  wet  one,  will  fail  to  explode  if  fire  reaches  it,  and  there  is 
no  reason  why  the  fire  should  not  reach  it  if  the  fuse  is  good  and 
has  been  properly  handled.  Nevertheless  cap  manufacturers, 
like  other  manufacturers,  are  blamed  for  failures  in  blasting 
and  are  called  upon  to  investigate  complaints,  but,  as  a  rule, 
the  difficulties  are  traced  to  improper  handling  by  the  operator, 


EXPLOSIVES  AND  THEIR  USE  191 

generally    unintentionally,    sometimes    through    lack    of    proper 
instructions. 

Caps  have  failed  to  explode,  although  the  fuse  had  apparently 
burned  all  right.  Upon  investigation  it  has  invariably  been 
found  that  the  fuse  had  not  been  put  all  the  way  into  the  cap, 
and  it  had  been  crimped  hard  near  the  end  with  some  objection- 
able tool  which  had  made  a  groove  around  the  shell  and  had 
choked  the  fire  in  the  fuse  so  that  it  could  not  spit  into  the  cap, 
Fig.  120.  Upon  removing  the 


old   fuse   and   putting   a    fresh     i» 

piece  into  the  same  caps  which  ^IG-  12°- 

had  failed  before,  but  crimping  them  with  a  broad-face  tool,  every 

one  has  exploded.     Hence,  to  avoid  choking  the  fire  in  the  fuse, 

always  see  that  the  fuse  is  pushed  down  into  the  cap  as  far  as 

the  composition  and  secured  to  the  cap  with  a  broad  tool,  making 

a   flat   compression   around    the    shell,    Fig.    121.     Avoid    thin 

crimpers,  which  make  a  groove  around  the  shell,  Fig.  122. 


FIG.  121.  FIG.  122. 

FIGS.  120-122.  —  Good  and  bad  forms  of  inserting  fuse  in  caps. 

Good  Crimping  Desirable.  —  Why  does  a  tool  which  makes  a 
groove  around  the  shell  frequently  choke  the  fire  in  the  fuse,  or 
cause  the  fire  instead  of  spitting  into  the  cap  to  break  out  through 
the  fuse  just  above  the  cap,  Fig.  122? 

The  familiar  Chinese  firecracker  will  serve  as  an  illustration. 
It  is  a  core  of  meal  powder  rolled  up  in  many  layers  of  paper  and 

choked  at  the  bottom.  The 
burning  powder  reaches  this 
choke  and  can  get  no  farther, 
so  it  takes  the  line  of  least 
resistance,  bursts  through  the 

side  of  the  paper  and  makes  the 
FIG.  123.  —  Type  of  crimper.  .,    .         ... 

desired  report.     So  it  is  with 

fuse;  the  choke  weakens  or  stops  the  fire,  according  to  how  hard 
it  is  crimped  and  how  near  the  choke  is  to  the  extreme  end  of 
the  fuse.  A  broad  crimper,  Fig.  123,  cannot  choke  the  fire 


192 


ROCK  DRILLS 


because  it  acts  similarly  to  a  vise,  and  any  good  fuse  will  burn 
through  a  pressure  of  300  Ibs.  in  a  vise. 

There  are  a  great  many  more  tools  on  the  market  which  have 
the  thin  crimping  part  than  have  the  broad.     The  thin  ones, 

Fig.  124,  have  been  cheaper  to 
get  up,  hence  find  a  market,  but 
invariably  wherever  replaced  by 
a  broad  tool  the  most  frequent 

source  of  misfiring  has  ceased. 

FIG.  124^- Type  of  crimper.  Miners  should  be   cautioned 

also  about  some  combination  crimpers  and  fuse  cutters,  because 
although  many  have  the  broad  crimper,  in  some  it  is  placed 
behind  the  cutting  part.  This  is  not  a  good  arrangement  be- 
cause the  cutter  comes  in  the  most  convenient  place  to  nip  the 
cap  with  when  in  a  hurry  and,  being  sharp,  not  only  makes  a 
groove  part  way  around  the  shell  but  also  breaks  the  shell  and 
lets  water  into  the  cap.  Bad  results  have  been  traced  to  this 
very  thing;  hence  operators  desiring  combination  tools  should 
be  particular  to  use  only  those 
which  have  the  cutter  behind 
the  crimping  part,  Fig.  125. 

When  the  use  of  a  crimper 
is  suggested  to  some  miners,  or 
when  they  hear  of  misfiring  FIG.  125.  -  Type  of  crimper, 

being  caused  by  poor  crimpers,  they  smile  and  tell  how  they  get 
along  by  merely  biting  the  cap  to  the  fuse  with  their  teeth.  This 
is  a  crude  method,  but  a  positive  admission  of  the  necessity  of 
fastening  caps  some  way,  or  else  these  fellows  would  not  take 
such  a  risk  of  putting  dangerous  things  in  their  mouths.  They 
also  admit  of  occasional  misfires  due  to  caps  slipping  away  from 
the  fuse  when  they  didn't  bite  hard  enough,  perhaps,  and  all  are 
familiar  with  " miners'  headaches,"  taking  them  as  a  matter  of 
course,  even  after  losing  time  waiting  for  noxious  gases  to  clear 
after  firing;  hence  these  blasters  have  all  this  time  unconsciously 
not  been  getting  the  best  results  out  of  caps  and  powder,  because 
good  crimping  not  only  secures  the  position  of  the  cap  and  keeps 
dampness  out,  but  also  serves  as  additional  confinement  to  the 
fulminate,  thereby  developing  greater  power  from  the  cap,  which, 
as  has  already  been  shown,  produced  a  correspondingly  increased 
result  from  the  powder. 


EXPLOSIVES  AND  THEIR  USE  193 

Proper  Care  of  Fuse.  —  Other  instances  of  complaint  have 
been  noted  where  the  end  of  the  fuse  inserted  in  the  cap  had 
become  damp.  It  had  burned  apparently  down  to  the  cap,  but 
in  so  doing  had  forced  the  hot  moisture  into  the  cap,  thereby  not 
only  moistening  the  fulminate  but  weakening  the  spit  of  the  fire 
from  the  fuse.  Damp  fuse  has  been  observed  to  burn  a  few  feet 
and  then  slow  down  or  hang  fire  and  sometimes  to  go  out.  Cut- 
ting off  the  burned  part  immediately  and  relighting,  the  remainder 
burned  a  few  inches  and  again  went  out,  and  so  on  through  the 
whole  length,  showing  conclusively  that  the  heated  dampness 
steamed  the  powder  enough  to  weaken  and  at  times  to  put  out 
the  fire.  The  remedy  is  as  follows:  Fuse  should  not  be  left  lying 
around  in  a  damp  place;  but  if  it  has  had  to  be  for  a  short  while, 
cut  off  a  few  inches  and  throw  the  piece  away,  or,  having  cut  off 
the  desired  length  for  the  whole,  always  put  the  freshly  cut  end 
into  the  cap.  Of  course,  caps  must  be  kept  dry  also. 

The  question  has  been  asked,  "Why  should  fuse  so  well  pro- 
tected with  waterproof  covering  dampen  so  readily?"  Because 
the  meal  powder  in  the  fuse  is  very  hygroscopic,  drawing  moisture 
from  the  atmosphere.  Also,  the  yarn  core  along  which  the  pow- 
der is  strung  is  very  dry  and  spongy,  so  that  both  the  powder 
and  yarn  will  draw  moisture  a  long  way  into  the  fuse. 

That  this  moisture  is  driven  ahead  of  the  fire  in  the  fuse, 
steaming  and  weakening  it,  has  been  demonstrated  in  still  another 
way  by  placing  one  end  of  the  damp  fuse  in  a  cold  glass  tube  and 
observing  the  large  amount  of  water  vapor  condensed  in  the  cold 
tube.  Dry  fuse  will  spit  fire  several  inches  into  the  tube  and  the 
glass  will  be  comparatively  free  from  water,  but  damp  fuse  will 
only  spit  very  weak  fire,  if  any  at  all,  and  the  cold  glass  tube  will 
be  wet  with  drops  of  condensed  steam  from  the  fuse,  the  amount 
of  moisture  increasing  with  the  length  of  fuse  burned. 

In  other  instances  blasters  have  smeared  double-tape  fuse 
with  vaseline,  others  with  axle  grease  or  crude  oil,  when  working 
in  wet  ground,  intending  to  make  it  waterproof,  and  these  oils 
being  solvents  of  tar  had  penetrated  the  tar  into  the  core  of 
powder  in  the  fuse  and  spoiled  it.  The  quantity  of  volatile 
tar  products  from  the  burning  fuse  may  also  be  observed  in 
the  glass  tube  mentioned  above  by  a  brown  stain  which  their 
condensation  will  make.  Soap,  clay,  or  tallow  will  protect  the 
fuse  for  a  short  time,  but  these  occasionally  get  chafed  off  when 


194 


ROCK   DRILLS 


pushed  into  the  hole  or  during  tamping.  Candle  grease  is  often 
used  and  is  efficient,  but  care  must  be  taken  not  to  apply  it  too 
hot.  The  safer  and  better  way  in  such  cases  is  to  use  triple-tape 
or  other  waterproof  fuse  in  wet  ground,  and  secure  the  cap  with 
a  broad  crimper,  or  wrap  about  four  inches  of  electricians'  adhesive 

tape  over  the  junction  .of  cap 
and  fuse,  Fig.  126.  In  very  wet 
^und  it  is  often  expedient  to 
use  electrical  exploders,  Fig.  119. 
Procuring  a  Complete  Detonation.  —  Unbottomed  holes,  "  stink- 
ers" and  premature  blasts  are  sometimes  complained  of.  These 
have  been  found  to  be  cases  either  of  (1)  using  too  low  a  grade  of 
cap  for  a  particular  kind  of  powder,  (2)  spoiled  powder,  (3)  care- 
less loading,  or  (4)  hole  cut  off  by  a  previous  shot.  The  proper 
choice  of  detonator  will  remedy  the  first  cause:  3X  or  4X  caps 
are  recommended  for  straight  dynamites  when  not  frozen;  5X, 
6X,  or  Lions  for  gelatine  dynamites,  chlorate  mixtures,  and  all 
other  inert  powders.  In  cold  weather,  nitroglycerine  powders 
become  less  sensitive;  the  shortest  cap  is  then  especially  recom- 
mended as  it  will  get  most  work  and  least  fumes 
out  of  any  powder,  even  under  favorable  condi- 
tions. 

The  second  cause  requires  more  careful  stor- 
age of  powder.  Nitroglycerine  evaporates  percep- 
tibly at  a  temperature  of  110°  F.,  so  that  the 
powder  will  become  weakened  and  somewhat 
inert.  It  freezes  at  about  42°  F.,  becoming  hard, 
inert,  and  dangerous.  In  a  damp  place  it  will 
absorb  moisture,  which  displaces  the  nitroglycer- 
ine, and  if  stored  there  for  any  length  of  time 
will  spoil.  Hence  dynamite  should  be  soft  and 
dry,  stored  in  a  dry  and  cool  place,  with  the  cases 
placed  so  that  the  sticks  of  powder  lie  flat  —  not 
on  end. 

As  for  the  third  cause,  premature  blasts,  smoky 
blasts,  and  weak  shots  frequently  result  when  the 
cap  is  buried  far  down  in  the  mass  of  the  charge, 
because  the  fuse  in  burning  down,  and  before 
reaching  the  cap,  may  prematurely  ignite  the 
powder  by  side  spitting  or  even  by  its  own  heat,  and  burn  up  part 


« 

t///'/\ 

FIG.  127.— Fuse 
placed  too 
deep  in  pow- 
der, causing 
powder  to 
burn  before 
exploding. 


EXPLOSIVES  AND   THEIR  USE 


195 


of  it  before  the  rest  explodes  (Fig.  127).  Even  in  preparing  a 
short  piece  of  cartridge  as  a  primer  it  is  bad  practice  to  push  any 
of  the  fuse  into  the  powder,  especially  if  it  is  cotton  covered,  as 
this  absorbs  nitroglycerine  rapidly,  which,  if  injected  into  the  cap, 
greatly  weakens  its  explosive  force,  and  sometimes  causes  misfire. 
Side  spitting  is  not  always  the  fault  of  the  fuse.  In  rough 
handling  it  may  have  become  kinked  and  the  tape  cracked  or 
j^  weakened  at  that  place,  so  that  it  blows  out  of 

the  side  of  the  fuse.  Hence,  never  bury  a  cap 
and  fuse  beneath  several  sticks  of  powder.  The 
cap  must,  however,  be  in  actual  contact  with 
the  powder,  hence  the  advisability  of  always 
tying  the  cap  and  fuse  into  the  last  stick  of 
powder  placed  in  the  hole,  Fig.  128,  so  that  the 
powder  cannot  slip  away  from  the  cap,  in  which 
event  there  would  either  be  tamping  or  an  air 
space  between  the  cap  and  charge,  both  of  which 
cause  mis-shots  or  bad  fumes  in  the  mine,  be- 
$  cause  when  the  cap  gets  separated  from  the 
powder  it  cannot  possibly  exercise  its  full  deto- 
nating effect. 

Suggestions  to  Insure  Best  Results  in  Blasting. 

FIG.  128.     Cor-     — jn  vjew  of  the  importance  of  the  facts  which 
rect    way    to 
place  cap  and     have  been  brought  forward,  a  summary  is  offered, 

fuse<  not  with  the  desire  to  dictate  hard  and  fast 

rules  to  those  who  are  breaking  ground  nearly  every  day  of  their 
lives,  but  in  the  form  of  brief  and  specific  suggestions  to  insure 
more  thorough  detonations  of  powder  and  best  results. 

First  —  Select  the  right  fuse  for  the  kind  of  work,  and  proper 
caps  for  the  kind  of  powder  in  use,  and  see  that  both  are  thor- 
oughly dry. 

Second  —  Powder  must  not  get  shaken  out  from  end  of  fuse, 
nor  sawdust  or  other  obstruction  get  in  between  fuse  and  cap 
composition.  Cutting  fuse  slanting  not  only  allows  a  little  of 

the  powder  to  shake  off,  but  .^.^^^  ^ 

often  makes  an  obstruction  to 

the  fire  because  the  slender  end     „      ,  0 ' ^lntol*rabl 

FIG.  129.  —  Wrong  way  to  cut  fuse, 
may  fold  under  Fig.  129.      Also 

a  sharp-pointed  piece  of  fuse  is  not  a  desirable  thing  to  thrust 
into  any  cap. 


196  ROCK  DRILLS 

Third  —  Cut  the  fuse  straight  across,  not  slanting,  and  push 
it  into  the  cap  half  an  inch  or  more,  all  the  way  down  to  the  pow- 
der, Fig.  121.  If  the  fuse  be  ragged  at  the  end  or  too  large  to 
enter  the  cap  easily,  never  peel  off  any  of  the  tape  or  yarn,  but 
swage  the  end  of  the  fuse  to  the  proper  size.  This  may  be  easily 

and  quickly  done  by  twisting 
and  squeezing  the  large  part 
with  the  crimper,  Fig.  130,  if  it 
be  a  broad  one.  Having  in- 
serted the  fuse,  squeeze  the 

shell  tightly  to  it  with  a  broad 
FIG.  130. -Swaging  end  of  fuse.          crimper     placed     around     the 

shell  so  that  one  side  just  overlaps  on  to  the  fuse.  This  will  make 
a  compression  about  a  quarter  of  an  inch  wide  around  the  ex- 
treme upper  end  of  the  shell. 

Fourth  —  The  blasting  powder  should  not  be  cold,  much  less 
frozen,  and  holes  should  be  carefully  charged,  squeezing  each 
cartridge  separately  with  a  wooden  rammer  so  as  to  fill  the  hole 
completely  to  the  desired  hight. 

Fifth  —  Having  crimped  the  cap  securely  to  the  fuse,  insert 
all  of  the  cap  —  but  none  of  the  fuse  —  into  a  stick  of  powder 

and  tie  together,  Fig.  131;  then  .^— * -?w-> 

put  this  priming  stick  upon  the      «         \ 


rest  of  the  powder  in  the  hole, 

Fig.  128,  and  do  not  ram  it  un-     FIG.  131.  —  Proper  placing  of  cap  in 

til  some  loose   sand  or  other  powder. 

tamping  has  been  put  in.     Use  tamping  without  any  sharp  rocks 

in  it  so  as  not  to  damage  the  fuse. 

Sixth  —  Wherever  a  whole  blast  may  be  fired  at  once,  and  for 
all  work  in  very  wet  places,  electrical  fuses  will  be  found  of  advan- 
tage. 

Caps  or  Detonators.  —  These,  as  shown  in  Figs.  119  to  122, 
consist  of  copper  vessels  about  1J  in.  long  and  22  caliber.  They 
contain  in  the  end  a  mixture  of  mercury  fulminate  and  potassium 
nitrate  or  chlorate;  when  used  for  electric  blasting  the  remainder 
of  the  capsule  is  filled  with  sulphur,  through  which  pass  the  two 
wires.  If  for  use  with  a  fuse  the  composition  in  the  end  is  covered 
with  shellac,  collodion,  or  paper.  In  America,  X  caps  contain 
3  gr.  fulminate  of  mercury;  XX,  6  gr.;  XXX,  9  gr.;  XXXX, 
12  gr.;  XXXXX,  15  gr. 


EXPLOSIVES  AND   THEIR  USE  197 

In  England,  by  law,  detonators  are  numbered  in  accordance 
with  the  charge  of  fulminate.  Nos.  1,  2,  3,  4,  5,  6,  7,  and  8  con- 
tain respectively  4.6,  6.2,  8.3,  10,  12.3,  15.4,  23.1,  and  30.9  gr. 
of  fulminate.  Dampness  reduces  the  strength  of  the  cap  enor- 
mously. The  filling  is  to  a  certain  extent  hygroscopic  and  absorbs 
moisture.  The  rock  driller  should  make  it  a  rule  always  to  keep 
detonators  in  a  dry  place,  and  never  to  use  detonators  that  have 
been  kept  open  to  the  air  for  any  time  underground  or  where 
the  air  is  damp. 

Electric  Detonators  are  made  in  two  styles,  high  tension  and 
low  tension. 

In  this  connection  I  take  the  liberty  of  reprinting  the  follow- 
ing article  on  "Group  Shot  Firing,"1  by  Sydney  F.  Walker. 

GROUP  ELECTRIC  SHOT  FIRING 

Group  shot  firing  with  electrical  fuses  is  somewhat  uncertain, 
and  as  explained  in  the  Engineering  and  Mining  Journal,  Feb- 
ruary 29,  1908,  the  uncertainty  is  due  to  differences  in  the 
fuses  themselves,  and  in  the  action  of  the  current  when  passing 
through  them.  There  are  two  forms  of  fuses,  and  in  both,  the 
fuse  cap  contains  a  small  quantity  of  a  detonating  substance, 
fulminate  of  mercury,  or  some  similar  ingredient.  In  one  form, 
fine  platinum  wire  is  embedded  in  the  detonating  matter,  and 
in  the  other,  two  small  copper  wires,  whose  ends  are  separated 
by  a  small  space,  are  also  embedded  in  it.  With  the  platinum 
wire  form,  which  is  known  as  the  low-tension  type,  the  neces- 
sary heat  to  produce  detonation  is  produced  by  a  current  of 
electricity  passing  through  the  wire,  and  heating  it  to  red- 
ness. With  the  other  form  the  heat  is  produced  by  a  spark 
passing  between  the  ends  of  the  two  copper  wires,  this  form  being 
known  as  the  high-tension  fuse.  The  low-tension  fuse  requires 
a  comparatively  large  current;  according  to  some  measurements 
I  made  some  time  ago,  about  0.3  amp.  per  fuse,  but  the  pressure 
required  is  small,  only  a  few  volts.  The  high-tension  fuse  requires 
but  a  small  current,  in  fact  I  do  not  know  of  its  having  been 
actually  measured,  for  it  would  be  difficult  to  do  so  as  it  possesses 
the  oscillating  properties  of  the  spark,  but  requires  a  compara- 
tively high  tension.  Much  of  the  trouble  with  fuses  that  occurred 
some  years  ago  was  due  to  the  fact  that  the  high-tension  fuses 
1  Eng.  and  Min.  Journ.  June  20,  1908. 


198  ROCK  DRILLS 

were  not  made  to  gage.  The  tension  required  to  throw  a  spark 
across  the  gap  between  the  wires  is  as  a  rule  fairly  high,  but  it 
will  necessarily  vary  with  the  distance  between  the  ends,  and  it 
may  also  vary  with  the  nature  of  the  substance  in  which  the  wires 
are  embedded,  and  with  the  manrier  in  which  the  substance  is 
packed.  In  the  tests  which  I  made  it  was  found  that  occasion- 
ally a  fuse  could  be  exploded  with  as  low  a  pressure  as  two 
volts,  while  on  the  other  hand,  some  require  as  much  as  100 
volts  to  explode  them.  Modern  fuses  have  followed  the  course 
of  the  general  improvement  in  engineering  work,  and  are  now 
made  more  nearly  alike,  and  therefore  there  is  considerably 
less  difference  between  the  individual  high-tension  fuses  than 
formerly. 

The  Necessity  of  Considering  All  Details.  —  A  little  considera- 
tion, however,  will  show  how  small  differences,  either  in  the 
lengths  of  the  platinum  wires  of  the  low-tension  fuses,  or  in  the 
gage  of  the  wire,  or  in  its  attachment  to  the  ends  of  the  copper 
leading  wires,  will  cause  a  considerable  difference  between  the 
circuits  that  are  open  to  the  current;  similarly,  small  differences 
in  the  distances  between  the  wires  of  the  high-tension  fuses,  and 
between  the  packing  of  the  detonating  substance,  will  also  lead 
to  considerable  differences  in  the  paths  offered  by  them.  If 
fuses  are  arranged  in  series,  the  danger  is,  with  the  low-tension 
fuses,  that  one  of  them  will  go  before  the  others  have  had  time 
to  receive  sufficient  current  to  cause  detonation,  and  then  the 
fuses  which  have  not  ignited  their  charges  cannot  do  so.  With 
fuses  connected  in  parallel,  that  is  to  say,  where  the  current  from 
the  exploder  divides  between  the  different  fuses  of  the  group, 
the  same  difficulty  may  arise  in  another  form.  If  one  of  the 
fuses  is  of  a  much  lower  resistance  than  the  others,  it  may  take 
so  much  current  from  the  firing  battery,  that  the  pressure  of  the 
current  delivered  to  the  others  is  not  sufficient  to  drive  the  neces- 
sary heating  current  through  them,  and  hence  they  cannot  ignite 
their  charges.  With  the  high-tension  fuses,  when  connected  in 
series,  there  is  not  the  danger  of  the  circuit  being  broken  by  one 
fuse  going  before  the  others  explode,  unless  the  explosion  also 
breaks  the  connecting  wires,  which  is  possible.  The  danger  in 
this  case  is,  that  one  or  more  of  the  fuses  may  be  of  such  resistance 
that  a  large  portion  of  the  pressure  is  absorbed,  and  only  one  or 
two  of  the  group  may  be  able  to  have  a  sufficient  pressure  to. 


EXPLOSIVES  AND  THEIR  USE  199 

throw  the  necessary  sparks  across.  When  high-tension  fuses  are 
arranged  in  parallel,  there  is  not  this  danger,  but  there  is  still 
the  possibility  that  some  of  the  fuses  may  be  of  too  high  a  resist- 
ance to  allow  a  spark  to  pass,  and  therefore  cannot  fire. 

The  trouble  is  often  accentuated,  as  is  stated  in  the  "  colliery 
notes,"  by  the  magnetism  of  the  firing  battery  having  been 
reduced.  This  is  one  of  the  troubles  encountered  in  the"  con- 
struction of  the  magneto-electric  machines,  that  are  now  so  uni- 
versally employed  for  firing  batteries;  but  on  the  other  hand,  the 
improvements  which  have  taken  place  in  the  manufacture  of 
special  magnet  steel  should  have  practically  neutralized  this 
difficulty.  Within  the  last  ten  or  fifteen  years  the  demand  for  a 
steel  that  will  accept  a  large  amount  of  magnetism,  and  what  is 
more  important,  that  will  hold  it  at  practically  the  same  limit  of 
saturation,  for  electrical  measuring  instruments,  has  been  followed 
by  the  usual  result,  and  manufacturers  are  now  able  to  produce 
a  thoroughly  satisfactory  steel  for  the  purpose.  Steel  made  for 
this  purpose,  the  writer  understands,  is  alloyed  with  tungsten,  and 
thoroughly  satisfactory  material  has  been  obtained. 

There  is  another  source  of  trouble  which  I  believe  is  the  cause 
of  some  of  the  failures  of  group  firing.  When  two  or  three  pieces 
of  electrical  apparatus  are  connected  in  series,  it  often  happens 
that  a  leak  connection  is  made  to  earth,  of  a  greater  or  less  resist- 
ance, and  the  wires  connecting  the  different  pieces  of  apparatus. 
It  is  found,  for  instance,  where  incandescent  lamps  are  run  in 
series,  that  sometimes  the  positive  lamp  of  the  series  will  burn 
more  brightly  than  the  remainder,  and  will  consequently  have  a 
shorter  life,  the  explanation  being  that  there  is  a  partial  ground 
beyond  the  first  lamp,  and  consequently  the  current  passing  to 
the  second  and  subsequent  lamps  is  less  than  that  passing  to  the 
first  lamp.  The  same  thing  may  happen  in  the  matter  of  fuses. 
Coal  is  not  a  good  conductor,  but  if  some  of  the  connecting  wires 
touch  it,  it  may  make  a  sufficiently  good  connection  to  carry  off 
a  certain  portion  of  the  current,  and  to  practically  reproduce 
the  conditions  mentioned  above,  in  connection  with  incandescent 
lamps. 

The  Importance  of  Care  and  Measurement.  —  The  remedy  for 
all  the  troubles  that  have  been  described,  in  the  " colliery  notes" 
referred  to,  and  in  this  article,  lies  in  care  and  measurement. 
One  of  the  great  advantages  that  electricity  possesses  is  the 


200  ROCK  DRILLS 

ability  to  take  measurements  with  comparative  ease.  It  is  always 
a  simple  matter  to  insert  a  measuring  apparatus  to  show  whether 
a  current  is  passing,  and  if  sufficient  money  is  spent,  the  actual 
strength  of  the  current,  or  the  actual  amount  of  the  pressure. 
One  of  the  precautions  that  could  be  taken  is  to  fix  a  small  cur- 
rent indicator  upon  the  case  of  the  firing  battery,  which  might 
be  graduated  to  show  approximately  when  the  current  passes  for 
one,  two,  or  more  fuses,  when  connected  in  parallel,  and  it  might 
also  be  arranged  to  show  the  pressure  available  from  the  battery, 
before  the  connection  was  made  to  the  wires  leading  to  the  fuses. 

The  objection  to  the  addition  of  such  an  apparatus  is  two- 
fold: it  increases  the  expense,  and  it  makes  something  additional 
to  get  out  of  order;  the  expense,  however,  will  be  well  incurred 
if  it  enables  the  shot-firer  to  have  a  more  complete  command  of 
his  shots  than  he  has  at  present.  The  additional  cost  of  a  current 
and  pressure  indicator  would  not  be  very  great;  and  if  each  shot- 
firer  always  had  the  same  battery,  he  could  become  so  familiar 
with  the  apparatus  as  to  be  able  to  read  with  considerable 
accuracy  what  has  taken  place  in  the  shot  holes. 

Possible  Improvements.  —  Another  point  where  improvements 
might  be  made  is  in  the  size  and  quality  of  the  wire  employed 
for  connecting  the  firing  battery  to  the  wires  leading  into  the 
fuses,  and  the  wires  attached  to  the  fuses  themselves.  The  idea 
has  prevailed  that  small  wires  and  poor  insulation  is  sufficient 
for  the  purpose,  and  the  view  is  correct  up  to  a  certain  point. 
If  only  one  fuse  is  to  be  fired,  the  problems  involved  in  the  size 
of  the  wire  and  its  insulation  do  not  come  in  appreciably;  but 
when  low-tension  fuses  are  to  be  fired  in  parallel,  the  size  of  the 
wire  may  have  an  important  bearing  upon  the  pressure  available 
for  the  fuses;  if,  in  addition,  there  is  a  partial  ground  taking  place 
between  the  fuses,  the  defect  already  mentioned,  the  cutting  off  of 
a  portion  of  the  current  from  the  second  and  following  fuses  may 
easily  be  brought  about.  The  insulation  of  the  wire  connecting 
the  battery  to  the  fuses,  and  of  the  wires  in  the  shot  hole  leading 
to  the  fuses  themselves  would  also  be  much  better  if  the  insula- 
tion was  higher  than  is  usual,  for  the  reasons  given  above.  The 
problem  involved  in  the  insulation  of  these  wires  is  somewhat 
similar  to  that  of  the  insulation  of  wires  for  electric  signals  in 
mines,  and  for  the  electric  bells  in  houses.  In  both  cases,  small 
wires  and  light  insulation  would  answer  perfectly  if  nothing  had 


EXPLOSIVES  AND  THEIR  USE  201 

to  be  considered  but  keeping  the  wires  clear  of  each  other,  off 
dry  wood,  and  if  the  wires  were  not  subject  to  damp,  rough  hand- 
ling. But  experience  has  shown  that  for  continuous  work  a 
large  wire  answers  best  in  both  cases,  and  a  comparatively  high 
amount  of  insulation;  the  same  reasoning  applies  to  the  wires 
employed  for  shot-firing.  If  the  wires  lying  on  the  ground  leading 
from  the  battery  to  the  shot  holes  are  well  insulated  there  will 
be  less  chance  of  the  wires  in  the  shot-holes  making  a  leak,  in 
case  they  touch  the  coal. 

Another  precaution  is  to  see  that  the  fuses  and  shot-firing 
batteries  are  tested,  both  before  going  down  the  pit  and,  as  far 
as  possible,  up  to  the  moment  of  firing  the  charge.  The  indicator 
suggested  above  will  answer  for  testing  the  battery;  immediately 
the  latter  shows  an  appreciable  loss  of  pressure  it  should  be  sent 
in  to  be  overhauled.  The  question  of  testing  the  fuses  is  a  some- 
what more  difficult  one,  but  by  no  means  insuperable,  with  the 
knowledge  of  electrical  apparatus  that  has  been  acquired  by  min- 
ing men  during  the  last  20  years.  The  low-tension  fuses  can 
be  tested  with  the  same  indicator  mentioned  above,  and  a  single 
dry  cell.  The  test  is  a  simple  one,  and  easily  carried  out.  A 
circuit  is  made  of  the  dry  cell,  the  indicator,  and  the  fuse,  and  the 
deflection  of  the  needle  of  the  indicator  should  be  noted.  It  is 
not  quite  sufficient  to  be  sure  that  the  circuit  is  complete  within 
the  fuse.  The  shot-firer  should  also  make  sure  that  the  circuit 
within  the  fuse  is  as  it  should  be,  and  the  indicator  will  show  this. 
As  explained  above,  when  the  shot-firer  gets  to  know  the  indicator, 
it  will  tell  him  all  about  every  fuse  that  passes  through  his  hands, 
and  he  will  know  quickly,  by  connecting  up  in  this  way,  whether 
or  not  the  fuse  is  good. 

Method  of  Testing  Fuses.  '- —  It  is  a  simple  matter  to  test  all 
fuses  when  they  arrive.  The  batch  of  fuses  that  are  taken  into 
the  pit  should  be  tested  before  going  underground,  and  they 
should  be  examined  the  last  thing  before  fixing  them  in  the  shot 
hole.  The  small  platinum  wires  are  exceedingly  delicate,  and 
apt  to  be  detached  from  the  copper  wires  to  which  they  are  con- 
nected. The  jolting  of  the  cage,  or  the  motions  of  the  man  who 
carries  them  as  he  walks,  may  cause  one  of  the  fuses  to  becom3 
disconnected. 

For  high-tension  fuses,  the  test  is  more  difficult,  but  can  easily 
be  arranged.  The  test  the  writer  suggests  is  a  resistance  test 


202  ROCK   DRILLS 

made  with  a  Wheatstone's  bridge.  The  Wheatstone's  bridge  is 
the  apparatus  employed  by  electrical  engineers,  in  various  forms, 
for  testing  resistances.  It  may  be  a  delicate  and  formidable 
apparatus,  and  is  so  when  arranged  for  delicate  laboratory  tests. 
But  on  the  other  hand,  portable,  knock-about  forms  are  made, 
arranged  so  that  tests  of  the  kind  suggested  can  easily  and 
quickly  be  carried  out,  and  with  sufficient  accuracy  for  the  pur- 
pose. A  somewhat  similar  series  of  tests  are  carried  out  in 
copper-smelting  works  in  the  United  Kingdom  for  the  purpose 
of  determining  the  purity  of  each  batch  of  copper  produced.  A 
small  sample  of  the  copper  is  taken  and  drawn  into  a  wire  of 
definite  length  and  of  prescribed  sectional  area,  and  this  is  con- 
nected to  two  terminals  of  a  Wheatstone's  bridge,  kept  in  the 
manager's  office;  in  this  way,  the  standard  of  the  copper  is 
quickly  obtained.  Each  of  the  filaments  of  the  millions  of  incan- 
descent electric  lamps  that  are  turned  out  are  tested  for  resist- 
ance by  a  similar  apparatus. 

Instrument  makers  will  have  no  difficulty  whatever  in  pro- 
ducing a  portable  apparatus  that  will  answer  the  purpose  described, 
and  shot-firers,  once  they  are  instructed,  will  have  no  difficulty  in 
testing  their  fuses,  before  taking  them  down  the  pit.  There  are 
two  dangers  in  connection  with  the  high-tension  fuse  that  a  resist- 
ance would  show.  The  copper  wires  may  be  too  far  apart  for 
the  available  spark  to  jump  the  space,  and  on  the  other  hand, 
the  wires  may  be  so  misplaced  that  there  is  no  space  to  jump. 
The  shot-firer  would  quickly  learn  to  diagnose  both  these  troubles. 
I  believe  that  if  the  above  is  followed  a  great  many,  if  not  all  the 
troubles  that  have  attended  group  firing,  will  gradually  disappear. 

Cautions  Regarding  Battery  Blasting.  —  The  following  points 
need  careful  attention  according  to  A.  and  Z.  Daw  in  The  Blasting 
of  Rocks. 

I.  That  the  battery  wire  and  detonators  are  suitable  to  each 
other. 

II.  That  the  battery  is  of  sufficient  power. 

III.  That  the  electric  fuses,  especially  high-tension  ones,  are 
stored  in  a  dry  place  and  that  all  gear  is  kept  dry  and  clean. 

IV.  That  the  joints  are  made  with  wire  that  is  bright,  and 
that  no  short-circuiting  takes  place. 

V.  That  the  wires  do  not  kink  or  twist  so  as  to  cut  the  insula- 
tion during  tamping. 


EXPLOSIVES  AND  THEIR  USE  203 

VI.  That  the   operator's   hand  or  any  other  conductor  does 
not  unite  the  terminals  of  the  battery  during  firing. 

VII.  That  the  battery  is  not  connected  to  the  cables  until 
everything  is  ready  and  all  persons  out  of  the  way. 

ELECTRIC  FIRING  vs.  FUSE  FIRING 

Simultaneous  explosions  of  holes  placed  in  such  a  manner  as 
to  take  advantage  of  it  are  beneficial  in  certain  cases.  Such 
cases  occur  generally  in  quarrying  by  the  bench  system.  In 
coal  mining  electric  firing  avoids  the  dangers  of  explosions  due  to 
the  ignition  of  fuses.  In  underground  mining  with  hard  rock 
headings,  the  cut  holes  are  fired  together  by  concussion  from  the 
first  charge  going  off.  The  other  holes  are  fired  separately. 
Robert  N.  Bell  gives  the  following  account  of  a  selective  electrical 
fuse-spitting  device  which  seems  to  offer  many  advantages  and 
to  be  worthy  of  adoption  in  many  instances. 

"The  device,  Fig.  132,  described  in  the  following  paragraphs 
was  perfected  at  the  Hecla  mine  in  the  Coeur  d'Alene  district, 
Idaho,  for  selective  firing  of  holes  from  a  distance  by  means  of 
electric  current. 

11  One  Miss  in  a  Thousand  Shots.  —  The  first  device  used  was 
not  satisfactory,  but  by  rebuilding  it  and  using  a  higher  voltage, 
P.  C.  Schools,  electrician  at  the  mine,  has  succeeded  in  bringing 
the  machine  to  such  a  state  of  perfection  that  the  misses  amount 
to  only  1  in  1000. 

"The  perfected  system  consists  of  a  firing  board,  where  the 
operator  tests  his  circuits  and  l  spits '  his  holes  in  the  order  desired ; 
a  reel,  on  which  is  wound  the  cable  carrying  the  wire  used  in 
spitting;  and  firing  blocks  attached  to  the  end  of  the  cable.  The 
holes  are  charged  and  primed  in  the  usual  way,  and  the  spitting 
wire  shown  in  the  accompanying  illustration  is  inserted  in  a  slit 
cut  in  the  fuse  near  its  end.  The  fuse  is  wrapped  tightly  with 
electrician's  tape,  and  thoroughly  coated  with  axle  grease,  so 
that  the  juncture  is  practically  waterproof  and  the  spitting  can 
be  done  successfully  under  water. 

"The  spitting  ends  are  all  prepared  before  going  into  the 
shaft  and  the  fuses  are  all  cut  the  same  length,  as  the  operator 
gives  the  time  interval  between  holes  when  he  inserts  the  plug 
at  the  firing  board.  Each  fuse  has  two  leads  of  a  spitting  wire 
projecting  from  its  end.  The  cable  containing  the  wires  with 


204 


ROCK   DRILLS 

Firing  Board 


Cable  down  Shaft 
(25  Wires) 

FIG.  132.  —  Device  for  selective  shot-firing  by  electricity. 


EXPLOSIVES  AND  THEIR  USE  205 

the  attached  firing  blocks,  which  is  kept  on  a  reel  in  the  station 
on  the  next  level  above  the  shaft  bottom,  is  now  lowered  to  the 
bottom,  and  the  two  No.  16  annunciator  wires  projecting  from 
the  fuse  of  the  first  hole  to  be  fired  are  securely  wrapped  around 
the  two  heavy  copper  leads  of  block  No.  1.  This  gives  hole 
No.  1  direct  connection  with  the  firing  board  on  the  level  above. 
Holes  Nos.  2,  3,  4,  etc.,  are  then  attached  to  the  numbered  blocks 
in  the  order  in  which  they  are  desired  to  explode. 

"The  system  shown  in  the  accompanying  illustration  is 
designed  for  a  24-hole  round,  which,  of  course,  can  be  used  for 
fewer  holes,  if  desired ;  the  number  of  holes  can  easily  be  increased, 
but  that  rarely  would  be  necessary. 

"  Tests  Insure  Ignition  of  the  Fuse.  —  When  all  the  holes  are 
ready  to  be  fired,  the  men  are  hoisted  to  the  firing  station,  and  the 
circuits  are  tested  out.  To  test  the  circuits,  the  main-line  switch 
is  closed  and  care  taken  that  the  single-pole  firing  switch  is  open, 
for  it  is  impossible  to  spit  a  fuse-  unless  the  firing  switch  is  closed. 
This  firing  switch  is  kept  in  a  box  Bunder  lock  and  key,  and  only 
one  man  on  each  shift  has  a  key  to  open  it.  The  flexible  cable 
and  plug  is  then  inserted  into  each  of  the  holes  in  the  firing  board 
numbered  to  correspond  to  the  holes  below  to  be  fired.  If  the 
circuits  are  closed,  and  ready  to  be  fired,  the  lamps  at  the  top  of 
the  board  will  light.  If  the  lamps  should  not  light,  then  there 
is  something  the  matter  with  the  circuit  that  must  be  remedied. 
If  all  the  circuits  test  closed,  then  the  shots  are  ready  to  be  fired. 

"To  fire  the  shots,  the  main-line  switch  is  closed,  the  firing- 
switch  box  is  unlocked,  and  plug  inserted  into  No.  1,  the  lamp 
lights,  the  firing  switch  is  closed.  This  short-circuits  the  lighted 
lamps,  causing  them  to  go  out,  and  at  the  same  time  applies  440 
volts  directly  across  the  No.  26  tinned  iron  wire  in  the  fuse  at 
the  bottom  of  the  shaft.  This  wire  melts  with  a  blinding  flash, 
spits  the  fuse,  and  burns  itself  free.  The  firing  switch  is  then 
opened  immediately,  so  that  if  an  arc  is  maintained  at  the  fuse  it 
will  be  smothered  by  the  cutting  in  of  the  lamp  resistance.  With 
the  plug  still  in  No.  1,  and  the  firing  switch  open,  failure  of  the 
lamps  to  light  indicates  that  the  spitting  wire  at  the  bottom  did 
its  work  and  the  fuse  is  now  burned,  but  if  the  lamps  again  light 
up  brightly,  it  indicates  that  the  fuse  did  not  spit  and  that  the 
firing  switch  must  again  be  closed.  It  is  seldom,  if  ever,  that 
the  firing  switch  has  to  be  reclosed. 


206  ROCK  DRILLS 

"Little  Additional  Time  Required.  —  The  operator  then  allows 
his  time  interval  —  a  few  seconds  between  holes  —  which  in  most 
cases  is  simply  time  enough  to  change  his  plug  to  the  next  hole. 
He  then  proceeds  with  the  second  hole  as  above  described,  retest- 
ing  the  circuit-firing  resistance  to  see  if  the  operation  was  success- 
ful, and  continuing  until  all  the  holes  are  spit.  The  melting  of 
the  fuse  wire  leading  to  each  hole  disconnects  the  firing  blocks 
so  that  the  lower  end  of  the  cable  is  free;  the  upper  end  is  then 
detached  from  the  firing  board,  the  cable  wound  on  the  reel, 
and  set  aside  until  the  next  round.  The  fuses  are  all  ignited  and 
the  shots  go  in  the  order  desired  without  any  attendant  danger. 

"While  seemingly  complicated  in  description,  this  device  can 
be  cheaply  installed  where  the  current  is  available.  In  making 
this  device,  nothing  is  required  besides  the  ordinary  material  and 
apparatus  kept  at  a  mine  where  electric  current  is  used  for  power. 

"This  device  is  as  simple  to  operate  as  a  telephone  switch 
board,  while  the  attaching  of  the  firing  blocks  to  the  fuse  takes 
little  more  time  than  would  be  required  in  spitting  a  fuse  with 
a  torch,  and  is  quicker  than  spitting  with  a  hot  iron,  but  of  course 
it  is  not  speed  that  is  important,  but  safety." 

Generally  speaking,  the  simultaneous  explosion  of  numerous 
holes  heavily  charged  with  high  explosives  would  have  an  unpleas- 
ant, not  to  say  disastrous,  effect  on  the  miners,  and  would  damage 
timbering  very  badly.  In  sinking  one  of  the  large  vertical  tim- 
bered shafts  on  the  Rand,  all  the  charges  were  fired  simul- 
taneously by  electricity.  The  effect  on  the  timbering  was  so 
disastrous  that  the  experiment  was  not  repeated.  In  wet  workings 
the  danger  of  short-circuiting  is  very  great.  When  shaft  sinking 
in  hard  ground,  using  heavy  charges  in  long  holes,  even  when  firing 
in  rotation  with  fuses,  the  accidental  simultaneous  discharge  of 
several  shots  always  resulted  in  damage  to  timbers.  Where  ground 
is  liable  to  give  trouble,  the  concentrated  shock  of  one  explosion 
of  numerous  charges  might  have  most  serious  consequences. 

GASES  RESULTING  FROM  THE  USE  OF  NITROGLYCERINE 
EXPLOSIVES 

W.  Cullen  states  l  that  the  complete  detonation  of  blasting 
gelatine  should  yield  only  carbonic  acid,  vapor  of  water,  and  nitro- 
gen;  but  in  practice  large  quantities  of  carbon   monoxide  are 
1  Journal  of  the  Chemical,  Metallurgical  Society  of  South  Africa. 


EXPLOSIVES  AND  THEIR  USE  207 

always  formed  even  under  the  best  conditions.  This  gas  acts 
as  a  slow  poison  on  the  human  system  even  if  inhaled  in  small 
quantities  over  a  long  period  and  if  it  exceeds  a  proportion  of 
more  than  0.1  per  cent,  in  the  atmosphere  it  may  cause  death. 
If  nitroglycerine  compounds  are  ignited,  nitrogen  peroxide, 
which  is  also  poisonous,  is  also  given  off  in  large  quantities  as  a 
red  vapor.  Small  quantities  of  this  gas  are  frequently  present 
after  an  ordinary  explosion.  The  burning  of  blasting  gelatine 
wrapped  round  a  stick  to  form  a  torch  should  not  be  allowed. 

In  ordinary  blasting  gelatine  the  ratio  of  CO  to  CO2  present 
in  the  air  after  blasting  was  1:6  to  1:8;  gelegnites  varied  from 
1:4.9  to  1:11.2.  Samples  of  air  were  taken  40  ft.  from  the 
face  immediately  after  blasting  in  an  unventilated  drive  and 
showed  percentages  of  CO  varying  from  0.467  per  cent,  to  0.88 
per  cent,  and  of  CO2  ranging  from  7.44  per  cent,  to  4  per  cent.  CO2 
is  an  inert  gas,  but  the  proportion  of  CO  caused  by  the  explosion 
of  about  50  Ibs.  of  blasting  gelatine  is  highly  dangerous. 

Mr.  Cullen  has  since  introduced  a  blasting  gelatine  in  which 
the  ratio  of  CO  to  CO2  has  been  reduced  under  actual  working 
conditions  to  1 :  16.7.  It  has  been  proved  that  the  paper  covers 
of  cartridges  help  to  produce  CO  and  that  CO  is  also  given  off 
by  the  burning  of  ordinary  safety  fuses. 

GASSING 

The  following  rules  for  procedure  in  cases  of  gassing  are  copies 
of  those  posted  on  mines  of  the  Transvaal  prepared  by  Drs.  Irvine 
and  Macaulay. 

Warning.  —  In  cases  of  gassing,  cold  water  must  be  avoided, 
as  its  application  will  further  increase  shock  and  lower  the  body 
temperature.  (Application  of  warm  clothing.) 

The  immediate  administration  of  whisky  or  brandy  is  also 
deprecated,  as  alcohol  increases  surgical  shock,  and  the  physiology 
of  shock  being  the  same  whatever  the  cause,  it  is  certain  that  it 
will  do  the  same  in  shock  from  gassing. 

Rules  to  be  Observed  in  Cases  of  Gassing.  —  (1)  In  every  case 
of  gassing,  the  matter  should  be  at  once  reported  to  the  shift  boss, 
and  by  him  to  the  manager. 

(2)  All  cases  must  be  kept  under  observation.  This  and  the 
preceding  rule  should  not  be  relaxed  in  any  case,  no  matter  how 
trivial  the  case  or  apparently  slight  the  initial  symptoms. 


208  ROCK  DRILLS 

(3)  Steps  must  be  immediately  taken  to  bring  the  sufferer  to 
fresh  air,  and  at  the  same  time  the  medical  officer  must  be  sent  for. 

(4)  Pending  the  arrival  of  the  doctor,  or  when  medical  ser- 
vices are  unprocurable,  the  immediate  steps  to  be  taken  in  cases 
of  gassing  are  as  follows: 

(a)  In  every  case  where  the  act  of  voluntary  swallowing  is 
possible,  an  emetic  should  be  at  once  administered,  and  for  this 
purpose  a  solution  of  sulphate  of  zinc  containing  thirty  grains 
to  the  ounce  is  kept  at  the  hospital.  This  is  to  be  administered 
in  ounce  doses  every  ten  minutes  until  vomiting  is  produced. 

(6)  Also,  a  supply  of  sal  volatile  (aromatic  spirits  of  ammonia) 
is  kept,  and  a  dose  of  two  drams  (two  teaspoonfuls  in  water)  are 
given  to  every  patient  who  can  swallow,  immediately  after  the 
completion  of  the  preceding  maneuver. 

(c)  For  severe  cases  of  gassing,  there  is  kept  at  the  hospital  a 
cylinder  of  oxygen  with  mask.     This  should  be  administered  in 
every  severe  case,   and  where  artificial  respiration  is  required, 
this  should  be  performed  in  an  unoxygenated  atmosphere. 

(d)  In  case  of  gassing  which  is  so  profound  as  to  cause  coma 
and  arrest  of  the  respiration,  artificial  respiration  must  be  started 
immediately,  and  persevered  with  so  long  as  there  are  indications 
of  life. 

Artificial  Respiration.  —  This  is  best  performed  by  Sylves- 
tor's  method,  which  is  as  follows:  The  patient  is  to  be  placed 
flat  upon  his  back  in  the  open  air  with  his  chest  and  arms  bare. 
A  pad  such  as  a  coat  rolled  up  is  to  be  placed  under  the  shoulders. 
The  tongue  must  be  brought  forward  so  that  it  does  not  fall 
backward  and  close  the  passage  to  the  windpipe.  The  operator, 
standing  at  the  head  and  looking  at  the  patient,  is  then  to  take  the 
arms  of  the  patient  by  the  wrist,  one  in  each  hand,  and  pull  them 
straight  out  beyond  the  patient's  head,  so  as  to  expand  the  chest 
as  much  as  possible.  By  now  doubling  the  arms  of  the  patient 
so  that  the  elbows  press  against  the  chest,  the  operator  must 
bring  the  patient's  arms  back  so  as  to  expel  the  air  from  the  lungs. 
He  makes  one  complete  motion  while  counting  one,  two,  three, 
and  the  operation  is  then  repeated  about  fifteen  times  per  minute. 

CHOICE  OF  EXPLOSIVES 

The  miner  is  called  upon  to  decide  as  to  the  most  suitable 
and  economical  explosive  to  employ.  Often  only  one  grade  of 


EXPLOSIVES  AND  THEIR  USE  209 

powder  is  employed  in  any  one  mine,  though  the  hardness  and 
composition  of  the  material  to  be  broken  may  vary  so  much  as 
to  make  it  possible  to  effect  economies  by  using  cheaper  varieties 
where  the  ground  is  softer.  The  following  factors  must  be  taken 
into  consideration:  (1)  The  cost  of  explosives  relative  to  the  cost 
of  drilling  holes;  (2)  cost  of  high-power  explosives  relative  to 
cost  of  lower  grades;  and  (3)  the  nature  of  the  rock  to  be  broken; 
whether  it  be  full  of  open  cracks  or  not,  and  whether  it  be  hard 
or  soft ;  whether  ore  broken  consists  of  brittle  high-grade  minerals 
such  as  argentiferous  galena  or  copper  ore,  which  shattering  explo- 
sives would  tend  to  powder,  thus  increasing  mining,  sorting,  and 
concentrating  losses;  or  whether  it  consists  of  hard,  tough,  low- 
grade  material  that  must  be  broken  to  a  certain  size  before  leaving 
the  mine. 

Generally  speaking,  if  the  ore  or  rock  is  hard  it  pays  to  use 
the  highest  grade  explosive.  Rock  drilling  becomes  a  great  item 
of  the  cost  of  extraction,  and  with  high  explosives  smaller  holes 
per  unit  of  rock  broken  can  be  bored.  If  the  hard  rock  is  being 
broken  in  comparatively  narrow  stopes,  with  two  faces  to  break 
to,  or  in  development  ends,  it  will  not  pay  to  bull  the  holes,  hence 
the  diameter  of  the  holes  will  have  to  be  increased  porportion- 
ately  with  lower  grade  explosives;  the  cost  of  drilling  depends 
largely  on  the  diameter  of  bit  used.  The  specific  gravity  of  the 
explosives  employed  must  also  be  considered,  since  the  power  of 
explosives  is  compared  on  unit  weights.  For  instance,  blasting 
gelatine  is  1.55  and  its  power  is  from  3.5  to  4  times  that  of  black 
powder  whose  specific  gravity  is  1.  Hence  a  chamber  to  contain 
an  equally  powerful  charge  of  blasting  gelatine  would  need  to 

have  only  a  cubic  contents  -—^ — — —  that  of  one  for  gunpowder. 

l.oo  X  3.5 

Several  powerful  explosives  are  really  useless  for  work  in  hard 
ground  because  they  are  light  and  take  up  too  much  space.  If 
the  rock  is  soft  with  numerous  heads,  boring  is  cheaper,  and  a 
less  expensive  low-grade  explosive  will  be  the  one  to  use.  The 
use  of  explosives  under  various  circumstances,  with  different 
rocks  and  ores,  is  referred  to  in  the  chapter  on  "Rock  Drill  Prac- 
tice." The  quarry  man  has  other  considerations  to  deal  with  in 
his  choice  of  explosives  which  do  not  concern  us  here. 


XI 
THE  THEORY  OF  BLASTING  WITH  HIGH  EXPLOSIVES 

I  HAVE  been  reading  most  of  the  works  published  on  blasting 
to  see  if  they  could  give  me  any  data  that  would  be  useful  in 
checking  the  work  done  in  breaking  rock  in  development  faces 
and  in  both  wide  and  narrow  stopes  in  our  mines.  I  think  it 
will  be  found  that  these  books  have  been  written  by  engineers, 
who  apparently  have  no  great  knowledge  of  underground  con- 
ditions, and  who  deal  with  the  subject  mainly  from  a  quarryman's 
or  railway  contractor's  point  of  view.  This  is,  I  think,  the  ex- 
planation of  the  fact  that  we  have  rules  laid  down,  based  appar- 
ently on  clearly  proved  mathematical  deductions  from  known 
forces  and  resistance,  which  any  right-thinking  miner  breaks 
every  day  of  his  life  for  obvious  economic  reasons.  Students 
of  this  subject  would  do  well  to  remember  that  whole  discussions 
and  theses  in  these  books  are  set  out  with  the  object  of  showing 
how  to  break  the  rock  with  the  smallest  possible  consumption 
of  explosives.  This  is  quite  a  secondary  consideration  with  the 
miner,  though  in  its  way  worthy  of  most  careful  consideration. 
The  miner's  object  is  to  raise  the  rock  to  the  surface  and  extract 
its  contents  with  the  minimum  total  costs  per  ton,  and  explosives 
are  only  one  item  of  costs.  So  we  need  beware  when  we  see 
theories  laid  down  solemnly,  ex  cathedra,  and  without  modifica- 
tion, for  instance,  in  regard  to  the  right  length  of  hole  to  be  bored 
in  certain  work;  for  no  attention  is  given  to  a  number  of  vital 
considerations  relative  to  saving  time,  and  therefore  to  total  cost 
of  the  work  to  be  done,  nor  to  several  obvious  methods  of  evad- 
ing in  practice  the  logical  conclusions  that  can  in  theory  be  drawn 
from  certain  mathematically  proved  theorems. 

A  general  knowledge  of  the  subject  is  necessary  in  order  to 
see  if  these  theories  can  be  applied  with  useful  results  under  local 
conditions,  and  if  they  point  out  any  directions  in  which  economy 
can  be  gained  in  the  use  of  explosives. 

Journal  of  the  Chemical,  Metallurgical,  and  Mining  Society  of  South 
Africa. 

210 


THEORY  OF  BLASTING  211 

Another  crying  need  of  the  industry  is  a  printed  sheet  to  be 
posted  up  on  all  mines,  giving  a  simple  and,  as  far  as  possible, 
non-technical  resume  of  everything  we  know  regarding  the  em- 
ployment of  high  explosives  in  boreholes  to  break  rock,  and  point- 
ing out  the  mistakes  miners  so  often  make,  and  the  reason  why 
they  are  mistakes.  Such  a  sheet  of  instructions  would,  I  believe, 
pay  for  its  cost  of  preparation  and  printing  in  a  month,  in  increased 
efficiency. 

The  subject  was  first  studied  practically  and  an  endeavor 
made  to  evolve  some  general  rules  drawn  from  my  own  experi- 
ence. I  have  since  found  that  the  few  laws  guessed  at  regarding 
direction  of  holes  and  charges  of  explosives  in  relation  to  the 
burden,  and  of  burden  in  relation  to  free  face,  were  in  the  main 
correct.  Readers  of  books  on  blasting  will  find  several  writers 
saying  the  theory  of  the  others  is  wrong.  Gillette,  in  his  "Rock 
Excavation,"  makes  some  shrewd  observations,  but  the  "Blasting 
of  Rock,"  by  Daw,1  if  read  in  the  light  of  practical  experience, 
and  by  people  ready  to  break  every  commandment  laid  down  in 
this  blasters'  decalogue,  to  save  time  and  money,  is,  I  think,  a 
valuable  book.  They  deal  with  the  following  points. 

Conditions  Influencing  Blasting.  —  Ten  conditions  are  first 
laid  down  which  influence  the  force  and  effect  of  a  blast.  They 
are,  presuming  that  a  hole  has  been  bored,  a  charge  inserted,  the 
hole  tamped  and  the  charge  detonated: 

(1)  The  size  and  number  of  the  free  faces  presented  by  the 
rock  mass.     For  instance,  a  drive  has  one  free  face  only;  a  stope 
has  two;  a  bench  on  an  open  cut,  after  the  center  hole  of  a  row 
has  gone,  has  three. 

(2)  The  tenacity  or  cohesive  strength  of  the  rock  (available 
to  resist  rupture  by  shearing). 

(3)  The    structure    of   the    rock,    whether   jointed,    massive, 
laminated,  stratified,  or  fissured. 

(4)  The  strength  and  nature  of  the  explosive  compound. 

(5)  The  character  of  the  fuse  and  tamping. 

(6)  The  thermal  conductivity  of  the  rock,  and,  I  might  add, 
of  the  tamping. 

(7)  Whether  the   blast   acts   alone,   or   simultaneously   with 
others. 

1  The  Blasting  of  Rock  in  Mines,  Quarries.  Tunnels,  etc.,  by  A.  W.  Daw 
and  Z.  W.  Daw.  (E.  and  F.  N.  Spon,  153.) 


212  ROCK   DRILLS 

(8)  Whether  the  rock  falls  when  broken,  or  has  to  be  lifted 
(by  the  force  of  the  blast). 

(9)  The  specific  gravity  of  the  rock. 

(10)  The  size  and  form  of  the  chamber. 

(11)  One  might  also  add  that  a  blast  is  influenced  by  the 
length  of  the  line  of  resistance,  in  proportion  to  that  of  the  hight 
of  the  free  face  and  of  the  length  of  the  hole  itself. 

Force  Generated  by  Explosives.  —  Daw  proves  without  diffi- 
culty that  the  old  time-honored  formula  L  =  CW3,  where  L  repre- 
sents the  weight  of  charge  (quantity  of  explosive)  necessary, 
and  where  W  =  the  line  of  resistance  or  the  shortest  distance 
from  the  charge  to  the  nearest  free  face  of  rock,  and  C  =  a 
coefficient  found  from  experiment  representing  the  relative 
resistance  of  the  particular  rock  to  rupture,  leaves  out  of 
consideration  most  of  these  factors,  and  is  useless  when  con- 
sidered by  itself.  The  force  generated  by  the  detonation  of 
explosives,  to  be  successful,  must  overcome  (a)  the  resistance  due 
to  the  cohesion  of  the  rock  tending  to  resist  rupture;  (6)  the 
resistance  due  to  the  mass  or  weight  of  the  rock.  This  is  not 
relatively  important  in  stoping,  and  where  the  rock  is  shot  down 
it  even  assists  rupture;  (c)  the  resistance  due  to  the  jambing  or 
hanging  of  the  rock  pieces  together  and  along  the  lines  of  frac- 
ture. The  force  must  act  at  90°  to  the  free  face  for  maximum 
results.  The  force  exerted  by  a  blast  on  the  rock  must  be  a  shear- 
ing force  and  not  a  bending  or  stretching  one,  because  the  explo- 
sive is  in  a  small  chamber  and  its  force  is  suddenly  applied  to  an 
inelastic  rock  mass.  The  force  required  to  produce  rupture  by 
shearing,  according  to  the  theory  of  mechanics,  where  P  =  force 
required  to  produce  rupture  and  S  denotes  the  periphery  of  the 
chamber  in  which  the  explosive  is  placed,  W  equals  the  line  of 
resistance  and  KI  =  a  factor  that  represents  the  comparative 
resistance  of  that  rock  to  shearing  as  determined,  say,  in  labora- 
tory in  ft.  Ib.  per  sq.  in.  =  the  modulus  of  shearing  for  the  par- 
ticular rock.  Then  P  =  SWK^ 

Daw  made  experiments  in  ice,  and  proves  that  this  formula 
holds  good  for  gradual  rupture,  and  he  proves  that  suddenly 
applied  forces  produce  similar  results.  The  question  that  he 
seems  to  have  neglected  to  investigate  is,  what  effect  varying 
the  size  and  shape  of  the  free  faces  has  in  regard  to  the  other  fac- 
tors? In  his  experiments  the  area  of  free  face  is  varied  within 


THEORY  OF  BLASTING  213 

very  narrow  limits.  He  never  defines  a  free  face.  This,  as  I 
will  endeavor  to  show  later,  seems  to  me  a  serious  omission,  when 
we  wish  to  apply  this  formula  to  actual  mining.  For  instance, 
we  have  a  hole  of  lj  in.  diameter  bored  in  the  face  of  a  stope 
which  is  6  ft.  high.  The  hole  is  6  ft.  deep,  bored  parallel  to  the 
face  of  the  bench.  The  burden  on  the  hole,  which  is  the  line  of 
resistance  =  W,  is  3  ft.  The  charge  occupies  2J  ft.  of  the  hole. 
P  =  SWKi  =  (1J  in.  +  30  in.  +  1J  in.)  X  36  in.  'X  modulus  of 
rupture  of  quartzite  to  shear.  The  area  of  the  free  face  at  right 
angles  to  the  line  of  resistance  W  is  then  6  X  6  =  36  sq.  ft.  Take 
the  same  hole  and  the  same  charge  in  a  stope  only  3  ft.  high; 
according  to  the  formula,  the  effect  should  be  the  same.  We  know 
very  well,  however,  that  the  first  hole  would  break  and  the  second 
one  would  never  break.  The  area  of  free  face  being  6X3,  or 
18  sq.  ft.,  in  the  second  case.  According  to  the  authors,  the  rock 
should  apparently  shear  in  a  plane  parallel  to  W  as  readily  as  it 
does  to  form  the  usual  frustum  of  a  pyramid  with  fracture  planes 
at  45°  to  W. 

With  due  deference  to  the  authors,  I  would  suggest  that  this 
formula  is  not  true  or  satisfactory  as  thus  stated.  It  is  true 
only  when  the  hight  and  length  of  the  free  face  bear  a  certain 
ratio  to  W  and  to  S,  so  that  the  limiting  lines  of  fracture  set  off 
from  the  perimeter  of  the  sides  of  the  chamber  at  an  angle  of  45° 
fall  within  the  area  of  the  free  face.  I  will  return  to  this  later  on. 
The  authors  then  point  out  that  with  two  free  faces  available 
(as  in  st oping),  two  portions  of  the  rock  may  be  ruptured  off  by 
shearing.  "  Owing  to  the  inelastic  nature  of  rock  and  the  sud- 
den force  applied,  equal  tension  is  produced  in  the  rock  parallel 
to  the  line  of  resistance  for  any  section  that  may  be  blasted/' 
and  that  the  resistance  to  rupture  of  the  cross-section  parallel 
to  the  line  of  the  hole  may  be  equal  to  the  resistance  to  shearing, 
and  should  be  so  to  prevent  "  bull-ringed "  holes.  If  F  repre- 
sents the  area  of  such  a  cross-section  and  K  the  modulus  of  rup- 
ture of  rock,  P  =  FK.  .'.FK=  SWKi. 

.  Hence  the  authors  argue  that  where  there  are  two  free  faces, 
any  hole  should  be  given  such  a  length  in  proportion  to  its  bur- 
den, or  W,  that  the  rock  lying  between  that  portion  sheared  off 
directly  in  front  of  the  charge  and  the  free  face  at  the  mouth 
of  the  hole  will  also  be  ruptured  off.  The  force  tending  to  produce 
rupture  in  blasting  is  proportional  to  the  periphery  of  the  cham- 


214 


ROCK   DRILLS 


her  containing  the  explosive,  such  periphery  taken  at  right  angles 
to  W,  or  line  of  resistance.  "The  section  of  rock  that  may  be 
ruptured  is  proportional  to  the  periphery  of  the  chamber  for  a 


FIG.  133.  —  Showing  how  this  rock  would  break  with 
high  explosive. 

given  line  of  resistance."  It  is  owing  to  the  condition  that  low 
explosives  are  employed  to  advantage  in  rocks  of  comparatively 
small  cohesive  strength,  or  where  there  are  many  lateral  free  faces 
and  joints.  These  are  used  in  large  holes  or  "bulled,"  or  "sprung" 
holes,  and  are  more  economical  than  high  explosives  in  small  holes. 


I 

r  /<c 

Hole  <3*-  wJ;  —  - 

^ 

FIG.  134.  —  Illustrating  proper  depth  of  hole. 

Thus  a  mass  of  rock  such  as  shown  in  Fig.  135,  with  high  explosives 
would  merely  break  a  crater,  as  the  cross- section  or  the  periphery 
at  the  top  and  bottom  of  the  charge  would  be  too  small  to  give 
sufficient  force  to  shear  the  rock  along  the  hole  and  beyond  it. 

It  seems  to  me  that  the  authors  have  neglected  the  rupturing 
effect  of  gases  from  the  charge  escaping  along  the  hole  between 
the  charge  and  the  mouth  of  hole.  This  must,  I  think,  have  some 


THEORY  OF  BLASTING  215 

effect  in  blasting;  a  larger  effect  with  low  explosives  and  a  smaller 
effect  with  high  explosives.  Those  who  have  seen  a  long  hole 
fired  have  noted  that  the  rock  from  the  mouth  is  shot  outwards 
quite  as  much  as  upwards,  apparently  by  a  force  acting  directly 
behind  it.  Regarding  most  mining  we  may,  I  think,  neglect  con- 
sideration of  the  resistance  due  to  the  weight  of  the  rock  blasted 
and  the  resistance  or  drag  of  the  fractured  rock  to  further  move- 
ment, though  occasionally  in  a  stope  we  do  see  where  a  hole  has 
had  a  charge  large  enough  to  fracture  the  rock  without  moving 
it.  When  previously  endeavoring  to  estimate  the  increase  of 
resistance  to  rupture  of  holes  due  to  increase  of  burden,  or  increase 
of  W,  I  hazarded  the  opinion  based  on  personal  experience  that 
this  increase  varied  as  the  square  of  the  burden  or  W2  for  the 
same  explosive.  The  authors  prove  this  to  be  true,  mathemati- 
cally. Now  we  see  why,  as  generally  conducted,  breaking  rock 
with  hand  holes  in  a  stope,  say,  48  in.  wide  is  much  more  economi- 


FIG.  135.  —  Showing  how  this  rock  would  break 
with  high  explosive. 

cal  in  explosives  than  breaking  the  same  ground  with  machines. 
The  6-ft.  machine  hole  carries  double  the  burden  of  the  3-ft.  hand 
hole,  but  requires  four  times  the  explosive  or  more,  and  the  ques- 
tion to  consider  is,  cannot  we  bore  and  blast  machine  holes  so  as  to 
reduce  this  difference?  The  authors  say,  "For  the  same  explosive 
the  resistance  of  cohesion  to  rupture  in  blasting  varies  as  the  square 
of  the  line  of  resistance."  But  here  again  we  note  that  no  consid- 
eration is  apparently  given  to  the  size  and  shape  of  the  free  faces; 
or  what  would  happen  if  the  face  is  only  partially  free,  as  in  a 
narrow  stope.  The  force  developed  by  an  explosive  placed  in  a 
chamber  in  the  rock  depends  on  the  following  conditions: 

(1)  The  absolute  quantity  of  the  gases  produced.     This  in 
turn  depends  on  the  quantity  and  " power"  of  the  explosive  used, 
and  I  would  add,  the  class  or  degree  of  detonation  produced. 

(2)  The  temperature  of  the  gases  at  moment  of  detonation. 

(3)  The  expansion  of  these  gases  due  to  heat  liberated  by  the 
chemical  combinations  started  by  detonation. 


216  ROCK  DRILLS 

(4)  The  time  occupied  in  obtaining  the  maximum  expansion 
or  pressure. 

(5)  The  size  and  form  of  the  chamber. 

(6)  The  thermal  conductivity  of  the  surrounding  medium. 
I  would  add  to  these  — 

(7)  The   amount   and   cohesion   of   tamping   employed   with 
certain  explosives. 

(8)  The  thermal  conductivity  of  such  tamping. 
Explosives  are  of  two  classes — "low"  or  slow  and  rending, 

and  "high"  or  quick  and  shattering.  Of  the  first,  gunpowder 
is  the  best  known  example.  The  explosives  used  here,  gelignite, 
gelatine  dynamite,  and  blasting  gelatine,  belong  to  the  latter 
class.  In  the  former,  chemical  combination  goes  on  compara- 
tively slowly  and  gases  are  evolved  gradually  and  at  a  low 
temperature.  In  the  latter,  the  substance  is  gasified  almost  in- 
stantaneously. "The  full  force  of  the  gas  is  at  once  exerted  in 
all  directions  and  upon  every  part  of  the  containing  body;  because 
motion  requires  time,  and  there  is  no  time  for  the  part  that  yields 
to  move  before  full  pressure  is  developed."  This  has  given  rise 
to  the  popular  idea  that  dynamite,  etc.,  acts  downwards.  Nitro- 
glycerine exerts  a  pressure  on  detonation  of  12,000  kilo,  per  square 
centimeter,  or  about  159,000  Ibs.  per  square  inch,  and  blasting 
gelatine  very  little  less.  Only  about  14  per  cent,  of  the  actual 
energy  of  the  explosive  is  employed  in  doing  useful  work  in  shat- 
tering and  displacing  rock.  This  seems  a  very  small  proportion; 
but  combustion  or  detonation  is  not  always  complete;  gas  escapes 
by  holes  and  a  lot  of  energy  in  the  form  of  heat.  Then  the  rock 
that  is  not  displaced  is  "shocked,"  heated,  and  pulverized,  and 
waves  of  force  are  sent  through  the  surrounding  rock  and  air. 
"If  we  assume  that  each  unit  of  the  same  explosive  compound 
will  develop  the  same  quantity  of  gases  and  attain  the  same 
maximum  pressure  under  like  conditions,"  two  laws  of  the  statics 
of  fluids  and  gases  help  us  to  judge  the  relative  force  developed 
by  an  explosive.  These  laws  are: 

(1)  That  the  pressure  exerted  by  a  fluid  upon  the  different 
parts  of  the  wall  of  the  containing  chamber  is  proportional  to  the 
areas  of  these  parts. 

(2)  That  the  pressure  exerted  by  a  fluid  in  any  direction 
upon  a  surface  is  proportional  to  the  projection  of  the  surface  at 
90°  to  the  given  direction. 


THEORY  OF  BLASTING  217 

Rock  is  inelastic,  the  limit  being  reached  in  most  rocks  with 
a  slight  change  of  form;  therefore  " there  will  be  no  appreciable 
enlargement  of  the  chamber  before  rupture  takes  place."  This 
is  laid  down  by  the  authors;  but  is  this  reasoning  quite  sound? 
We  know  blasting  enlarges  the  holes  by  reducing  the  walls  sur- 
rounding the  charge  to  an  impalpable  powder. 

This  is  done  either  before  rupture,  during  rupture,  or  after 
rupture.  It  cannot  well  be  after  rupture,  and  taking  the  case 
of  a  hole  that  fails  to  break  and  blows  out,  one  would  think  that 
the  gases  expend,  force  over  the  enlarged  area  before  they  seek 
exit  along  the  hole.  The  authors  in  speaking  of  cut  holes  seem 
to  concede  that  such  an  action  takes  place.  However,  let  us  take 
this  as  proved.  Then  it  follows  that  rupturing  force  P  produced  in 
any  hole  is  equal  to  the  maximum  pressure  produced  multiplied  by 
the  projection  of  the  chamber  at  right  angles  to  direction  of  rup- 
ture =  W.  Therefore  with  the  same  explosive  the  rupturing  force 
is  proportional  to  the  cross-sectional  area  of  the  chamber  at  90°  to 
W.  And  in  comparing  two  holes  having  the  same  charges  (which 
must  entirely  fill  the  chamber  to  develop  their  full  power),  that 
charge  which  is  in  a  chamber  having  the  greatest  area  at  90°  to  W 
in  proportion  to  its  size  will  do  the  most  work.  This  is  true,  how- 
ever, only  within  limits,  as  the  thermal  conductivity  of  the  rock 
may  absorb  too  much  power  in  a  very  thin  chamber.  Hence,  say 
the  authors,  f  in.  should  be  the  minimum  thickness  of  a  charge. 

Cylindrical  Holes.  —  It  will  be  seen  that  the  cylindrical  form 
of  chamber  as  bored  in  rock  by  a  drill  is  not  the  most  economical. 
If  we  could  put  the  charges  we  now  use  into  chambers  having  a 
thickness  parallel  to  the  free  face  double  that  of  their  depth,  we 
could  reduce  explosives  used  by  nearly  50  per  cent.  This  raises 
the  question:  What  is  the  effect  of  " chambering,"  "bulling,"  or 
"springing"  holes  in  hard  ground  in  narrow  stopes?  It  is  here 
generally  wasteful  in  explosives  and  not  at  all  useful,  as  we  require 
elongated  charges  for  the  best  results.  In  very  long  holes  in  softer 
ground,  in  quarrying,  and  in  very  wide  stopes  it  is  very  useful. 
The  authors  then  prove  that  in  blasting  tight  rock  where  joints 
and  fissures  are  not  well  developed,  the  diameters  of  boreholes 
should  be  directly  proportional  to  the  lines  of  resistance,  and  they 
state  that  they  have  proved  this  experimentally.  Working  .with 
gelatine  dynamite  in  strong  granite  which  approximates  the  con- 
ditions here,  they  give  the  accompanying  Table: 


218 


ROCK   DRILLS 
DIAMETER  OF  HOLE  PROPORTIONAL  TO  DEPTH 


Diameter 
Borehole 

Depth  of 
Borehole 

Length  of 
Charge 

Weight  of 
Charge 

Length  of  W 
Resistance  = 

=  Line  of 
Burden 

in. 

ft.           in. 

in. 

Ib. 

ft. 

in. 

1 

3          2 

9 

.22 

2 

4£ 

11 

6          3 

18 

1.75 

4 

9 

1 

4          2 

12 

.50 

3 

2 

2 

8           4 

24 

4.20 

5 

4 

In  softer  ground  Eissler  gave  1|  in.  dia.  for  5  ft.  (  =  W) 
"  "  "  "  H  in.  dia.  for  6  ft.  (  =  W) 
"  "  "  "  If  in.  dia.  for  7  ft.  (  =  W) 

The  diameters  given  here  are  proportional  to  the  length  of  W. 
In  mining  practice  this  is  a  principle  that  is  only  partially 
observed  and  which  deserves  further  attention. 

Ratio  of  Depth  to  Diameter  of  Hole.  —  I  pass  over  several 
interesting  chapters  on  simultaneous  blasts  and  turn  to  discuss 
what  length  charges  in  cylindrical  holes  should  bear  to  the  diam- 
eter of  hole  where  there  are  two  free  faces.  The  ratio- is  given 
from  8  to  I2d  where  d  =  diameter  of  hole.  If  there  are  two  free 
faces  an  elongated  charge  is  the  proper  one  to  employ,  not  a  con- 
centrated one  got  by  " bulling"  or  " chambering"  the  hole.  The 
authors  also  prove  that  when  we  find,  say,  8  in.  of  charge  suits  a 
hole  1  in.  diameter  to  move  a  burden  of  24  in.,  then  if  we  increase 
the  burden  to  36  in.  and  use  a  li-in.  hole  the  same  length  of  charge 
is  the  right  one. 

The  authors  next  consider  the  best  position  for  a  chamber 
or  charge  when  there  are  two  free  faces  at  right  angles,  as  in 
stoping.  To  obtain  the  best  effect  with  a  blast  in  rock  there 
must  be  equilibrium  of  resistance  on  all  sides  of  W  to  the  action 
of  the  charge. 

On  this  depends  the  right  depth  of  hole  to  bore,  say  the  authors, 
for  any  given  burden.  In  hard  ground,  the  distance  from  the 
center  of  an  elongated  charge  to  the  mouth  of  the  hole  at  right 
angles  to  the  line  of  resistance,  as  in  a  stope  bench,  should  be 
equal  to  the  burden,  or  W,  Fig.  134.  For  example,  we  have  a 
stope  6  ft.  high;  the  hole  has  a  burden  of  3  ft.;  the  charge  will 
equal,  say,  5  sticks  of  IJ-in.  gelatine;  the  hole  being  1J  in.  diame- 
ter at  bottom;  the  charge  takes  up,  say,  30  in.  of  the  hole.  What, 
according  to  the  author,  is  the  right  length  of  hole  ?  It  would  be 


THEORY  OF  BLASTING  219 

36  in.  +  15  in.  =51  in.  only.  In  practice  we  use  holes  60  to  72 
in.  Hence,  as  I  suggested,  pressure  of  gas  escaping  along  the 
hole  must  have  some  effect,  or  planes  in  the  rock  must  greatly 
affect  the  result. 

Formula  for  Calculating  Charges.  —  Formulas  are  given  for 
calculating  bore-hole  charges;  but  as  the  coefficients  Cv,  etc., 
for  the  various  rocks  met  with  in  different  mining  fields  are  not 
available,  it  would  be  useless  to  check  the  calculations  from 
actual  practice. 

The  formula  used  for  calculating  charges  where  L  =  weight 
of  charge  is  L  =  Cv  W3,  and  where  the  diameter  of  bore  is  known 
and  the  length  of  charge  used  is  n  times  the  diameter,  and  the 
weight  of  1  cu.  in.  of  explosives  in  Ib.  =  0.036  sp.  gr.  of  explo- 
sive, L  =  .0283  ngd3.  The  coefficient  Ca  in  the  formula  A  =  CaSW 
and  coefficient  Cv  in  the  formula  L  =  Cv  W3  are  found  by  trial 
shots.  These  are  taken  in  average  ground  on  average  benches 
as  nearly  similar"  as  possible.  Say,  3  holes  are  bored  with  bur- 
dens of  2  ft.,  2  1  ft.,  and  3  ft.,  and  are  1  in.  diameter  and  are 
charged  to  a  depth  of  8d  with  explosive.  Then  supposing  the 
hole  having  a  burden  of  2J  ft.  and  a  depth  of  2  ft.  10  in.  just 
breaks,  throwing  the  broken  rock  only  a  short  distance;  from  the 
equation  A  =  Ca  SW 

Ca  =  -.     A  =  8  sq.  in.     S  =  2  (8  +  1)  in.     * 


Then  Ca  =  -  =  .015.     Ca  =  .02  nearly  for  rocks  such  as 

quartzites  and  conglomerates. 

To  find  C,  in  formula  L  =  C,  W3,  W  =  2J  ft.     The  weight 

of  the  charge  L  in  ounces,  taking  the  specific  gravity  of  explosive 

(say,  dynamite  =  1.6),  the  weight  of  a  cubic  inch  of  dynamite  = 

.036  X  1.6  X  16  =  .9216  oz.  /.  L  =  .7854  X  .9216  X  8  X  (1  in.)2 

=  5.79  ozs.    Then  as  W  =  2J  ft., 

*-w-* 

Theoretically  these  formulae  should  enable  any  one  working  in 
homogeneous  rock  to  calculate  charges  in  all  cases. 

It  must,  however,  as  the  authors  point  out,  be  remembered 
that  benches  vary  in  shape  and  that  heads  or  planes  of  weakness 
are  nearly  always  more  or  less  developed.  The  art  of  blasting 


220  ROCK   DRILLS 

and  rock  drilling  consists  in  noticing  these  and  allowing  sufficiently 
for  their  presence,  and  in  correctly  forecasting  what  work  each 
individual  shot  will  do. 

Regarding  cut  holes  the  authors  in  this  paragraph  appear 
to  concede  my  contention  that  the  enlargement  of  a  hole  during 
detonation  of  charge  may  affect  the  area  over  which  the  gases 
exert  pressure.  "The  effect  of  breaking  in  cut-hole  shots  is 
greatest  if  they  meet  so  that  the  intervening  rock  is  fissured  and 
pulverized,  as  in  that  case  a  pressure  surface  for  the  gases  from 
the  explosion  will  be  produced  parallel  to  the  face  of  the  drive 
between  the  boreholes." 

Efficiency  and  Tamping.  —  The  authors  s&y,  in  general  it  is 
sufficient  to  use  a  tamping  of  water,  or  a  few  inches  of  clay  or 
paper  pushed  tightly  home  is  all  that  is  required. 

An  opinion  is  gaining  ground  that  water  is  not  an  efficient 
tamping  for  high  explosives.  Gillette  quotes  an  authority  as 
saying  that  it  takes  3  Ib.  of  dynamite  with  water  tamping  to  do 
the  work  of  1  Jb.  with  dry  tamping.  When  we  consider  the  enor- 
mous specific  heat  of  water  and  its  cooling  effect  in  the  gases 
produced,  this  seems  likely  to  be  true.  G.  M.  McFarlane,  in 
the  Engineering  and  Mining  Journal,  in  discussing  blasting  long 
holes  15  to  20  ft.  deep  says,  "The  remark  is  often  made  that 
water  is  the  best  tamping  for  dynamite.  As  a  matter  of  fact,  I 
note  that  in  ''springing"  or  ''bulling"  holes,  water  tamping  is 
always  blown  out,  even  if  the  hole  is  full  of  water,  whereas  7  or 
8  ft.  of  sand  tamping  is  seldom  blown  out,  unless  the  rock  is  very 
tough  and  the  bottom  dead  on  the  solid. 

He  also  states  that  the  detonation  of  dynamite  explosives  is 
due  to  the  pressure  developed  by  the  explosion  of  the  detonator 
acting  on  about  2  cu.  in.  next  detonation  and  that  the  transition 
from  solid  to  gas  takes  one  twenty  thousandth  part  of  a  second. 
He  calls  this  the  first  explosion  which  is  transmitted  to  the  rest 
of  the  charge  and  recommends  that  the  detonation  always  be 
placed  on  top  of  charge.  He  recommends  8  to  10  in.  of  clay 
tamping  except  in  cut  hole,  where  if  W  =  4  ft.  the  concussion 
would  take  one  two  thousandth  of  a  second  to  reach  surface. 
Gases  must  therefore  be  confined  for  that  time.  The  tamping 
would  be  subjected  to  a  pressure  in  a  If-in.  hole  of  450,000  Ibs., 
sufficient  to  force  18  in.  of  clay  tamping  6  in. 

In  boring  cut  holes  in  hard  ground  he  recommends  boring  holes 


THEORY  OF  BLASTING  221 

of  minimum  diameter  at  bottom  and  enlarging  them  by  "  spring- 
ing" with  about  four  sticks  of  60  per  cent,  dynamite. 

Recent  writers  have  recommended  placing  the  detonator  at 
the  bottom  or  center  of  the  charge,  and  H.  M.  Adkinson  adopted 
this  method  in  driving  the  Newhouse  tunnel.  The  consensus  of 
opinion  is  against  such  a  practice  and  any  benefits  gained  thereby 
are  offset  by  the  danger  of  igniting  the  charge.  Better  results 
might  be  gained  by  inserting  another  detonator  in  a  long  charge 
in  order  to  carry  the  wave  of  complete  detonation  to  the  bottom. 

Development.  —  Here  the  authors  have  not  much  to  say  to 
help  practical  miners.  "In  hard  and  tight  rock  the  best  length 
of  advances  (a  length  of  round)  with  each  set  of  holes  is  one- 
half  the  width  of  the  heading."  This  means  that  we  should 
bore  holes  only  3  to  4  ft.  long  in  the  faces  of  our  drives. 

"Experience  shows  that  from  f  to  1J  in.  is  the  best  diameter 
of  hole  to  use  in  breaking  hard  ground."  The  diagram,  Fig.  176, 
shown  for  the  advances  of  a  6i  X  6£  heading  shows  20  holes  bored 
3  ft.  4  in.  long  in  the  face  of  hard  rock.  These  holes  are  1J  diam- 
eter and  would  be  charged  to  a  depth  of  12  diameters  with  |  Ib. 
gelatine  dynamite,  giving  an  expenditure  of  15  Ib.  explosive  for 
an  advance  of  about  2^  ft.  to  3  ft.  These  20  holes  are,  the  authors 
tell  us,  fired  in  5  rounds  of  4  each.  This  of  course  would  be  im- 
possible in  most  cases  in  actual  mining  work,  owing  to  loss  of 
time  and  ventilation  difficulties.  I  give  this  example  to  show 
how  the  mining  student  must  beware  of  trusting  to  books  instead 
of  to  actual  experience.  On  the  Rand,  I  suppose  the  most  eco- 
nomical advance  for  such  a  heading  would  be  14  to  16  holes,  6  to 
7  ft.  long,  1^-in.  finishing,  using  about  50  Ib.  blasting  gelatine 
per  round,  and  firing  with  two  volleys  only.  The  diagram  for 
sinking  a  14  X  7  shaft  with  42  3£-ft.  holes  may  be  compared  with 
figures  given  in  Truscott's  Rand  mining  and  the  practice  in  shafts 
here. 

It  must  not,  however,  be  imagined  that  these  formula}  and 
axioms  are  valueless.  On  the  contrary,  a  knowledge  of  them 
rightly  applied  may  save  much  time  and  money  to  a  mine  and  its 
workers.  And  in  tunnel  and  quarry  work  where  a  skilled  engineer 
is  available  to  direct  the  depth  and  direction  of  holes  and  their 
charge,  large  economies  can  be  made.  The  idea,  however,  of 
a  miner  sitting  down  to  calculate  charges  is  a  vision  of  the  far 
distant  future.  Nevertheless,  it  is  true  that  the  so-called  skilled 


222  ROCK  DRILLS 

workers  of  the  Rand  and  elsewhere  waste  thousands  of  pounds 
of  explosives  every  month  by  boring  and  firing  holes  in  direct 
opposition  to  all  the  correct  principles  of  the  art.  Faces  of  drives 
have  rounds  hung  up  because  the  miner  has  neglected  to  bore 
enough  holes  to  make  W  bear  the  proper  proportion  to  the  length 
of  hole  and  the  charge. 

Size  of  Hole  and  Eight  of  Bench  Compared.  —  There  is  one 
example  of  the  application  of  these  rules  given  in  the  book  that 
bears  on  this  matter.  It  is  entitled  "  Economy  of  proportioning 
depth  and  diameter  of  borehole  to  height  of  bench  of  rock."  Sup- 
posing it  is  found  that  a  1-in.  hole  3i  ft.  long  with  burden  or  W 
—  3i  ft.  with  two  free  faces  (i.e.,  face  of  bench  in  which  holes  are 
bored  and  side  of  bench  or  stope  face)  when  charged  with  12  in. 
or  0.543  Ib.  of  dynamite  will  blast  a  bench  3?  ft.  long  (deep),  is 
there  economy  if  holes  of  1  in.  diameter  are  used  for  blasting  a 
bench  6  ft.  long?  Holes  required  will  be  6  ft.  deep.  W  will  be 
the  same,  and  there  must  be  the  same  length  of  tamping  or  vacant 
hole  in  each  case,  says  the  author.  Hence  the  charge  on  the  long 
hole  must  be  3?  ft.  long  and  must  weigh  1.9  Ib. 

Comparative  volumes  of  rock  broken  will  be  3.5  X  32  =  31 
cu.  ft.,  and  in  the  second  6  X  32  =  54  cu.  ft.  Then  in  both  cases 
we  have  0.111  ft.  of  rock  bored  per  cu.  ft.  blasted,  but  in  the  first 
case  we  use  only  0.017  Ib.  explosive  per  cu.  ft.  blasted,  and  in  the 
second  0.0352  Ib.  or  104  per  cent.  more.  "This  example,"  say 
the  authors,  "  shows  the  importance  of  boring  holes  on  correct 
principles  to  obtain  greatest  economy  in  explosives."  Trouble 
due  to  "bull-ringing"  occurs  in  holes  over  6  ft.  long  in  stoping 
on  the  Rand  in  some  cases.  These  examples  are  all  right,  and 
yet  all  wrong  if  applied  to  actual  mining  conditions.  In  mining, 
with  outputs  to  consider,  economy  of  explosives  is  a  secondary 
matter.  Longer  holes  pay  to .  bore  in  any  case,  as  thereby  less 
time  is  lost  rigging  up  and  adjusting  larger  machines. 

Engineers  have-  been  asking  if  they  would  get  any  better 
drilling  results  in  stoping  rock  with  higher  air  pressures.  They 
would  not  unless  pressures  were  increased  enough  to  give 
increased  boring  speed  of  20  per  cent.,  enabling  5  holes  to  be 
finished  from  one  set  of  the  drill  where  4  were  drilled  before,  or 
unless  miners  are  provided  with  longer  steel  enabling  them  to 
lengthen  their  4  holes  as  the  pressure  increased. 

Can  we  apply  any  of  the  foregoing  formulae  to  stoping  con- 


THEORY  OF   BLASTING  223 

ditions?  Take  this  case.  Right  of  stope  4  ft.,  no  good  heads 
or  defined  hanging  or  foot  wall.  What  is  the  right  diameter 
of  hole  to  finish  with?  What  is  the  maximum  burden  we  dare 
place  on  such  a  hole  in  hard  ground?  What  is  the  right  length 
of  hole  to  bore  so  that  both  faces  are  free  faces,  and  so  that  the 
hole  will  break  with  a  charge  suitable  for  diameter  of  hole?  If 
we  add,  so  that  the  rock  will  be  broken  in  the  cheapest  possible 
manner  with  due  regard  to  all  costs,  costs  of  labor,  power,  ex- 
plosives, capital  costs,  and  standing  charges,  we  have  here  a  prob- 
lem as  complex  as  any  the  human  intellect  has  ever  been  asked 
to  solve,  one  calling  for  the  exercise  of  the  highest  faculties  and 
involving  an  ever-widening  circle  of  factors  of  various  values, 
which  must  all  be  given  their  due  weight.  And  it  is  solved  largely 
by  rule  of  thumb,  or  rather  the  solution  is  evaded.  Yet  some 
people  call  the  mining  problem  here  a  simple  one! 

Now  taking,  Fig.  136,  a  roof  hole  H  with  W  =  4  ft.,  it  has  the 
faces  along  HM  and  NH  to  break  out,  and  theoretically  should 
break  direct  along  HN  =  W  =  4  ft.  by  shearing  a-s  easily  as 
along  HN1,  in  which  case  the  stope  would  need  to  be  8  ft.  high. 
We  know  that  with  a  hole  of  ordinary  1J  or  \\  in.  diameter, 
such  a  hole  would  never  break,  though  it  would  do  so  were  the 
stope  8  ft.  high.  Practice  here  seems  to  conflict  with  the  authors' 
theory,  unless,  as  I  suggest,  they  have  neglected  to  take  into  con- 
sideration the  size  and  shape  of  "free  faces." 

In  tight  ground  in  such  a  stope  about  24  in.  would  be  the 
maximum  burden,  =  W,  given  to  such  a  first  hole,  and  this  cor- 
responds to  the  greatest  value  of  W,  allowing  the  angle  of  the 
plane  of  cleavage,  due  to  the  explosion,  to  be  45°  on  each  side  of 
W.  When  there  is  a  line  of  bedding,  but  not  a  properly  defined 
hanging  wall  along  W,  then  W  might  be  made  perhaps  3  ft.,  and 
were  there  a  really  well-defined  parting  on  the  hanging  W  might 
even  equal  4  ft.  Theoretically,  by  using  a  large  hole  and  a  big 
charge  any  hole  might  be  broken;  but  this  is  not  true  in  practice. 

Long  vs.  Short  Holes.  —  Let  us  now  consider  the  case  of  long 
holes  versus  short  holes  in  stopes  of  moderate  width.  According 
to  the  theory  as  shown,  depths  of  holes  must  be  directly  propor- 
tioned to  the  resistance,  burden  or  W,  as  the  distance  from  cen- 
ter of  charge  to  mouth  of  hole  should  not  exceed  W.  In  practice 
here,  this  distance  is  generally  1J  to  If  W,  i.e.,  a  6-ft.  hole 
with  a  2|-ft.  charge  is  given  a  burden  =  W  =3  ft.  In  narrow 


224 


ROCK   DRILLS 


slopes,  however,  W  is  limited  entirely  by  the  hight  of  the  free 
face,  as  I  have  shown,  unless  the  hole  is  bored  a  size  that  is  un- 
economical. Holes  any  great  depth,  if  fired  in  the  usual  way, 
do  bull-ring,  i.e.,  fail  to  break  the  rock  near  the  collar  or  mouth 
of  hole  when  a  charge  is  placed  in  the  end  sufficient  to  overcome 
W.  I  was  formerly  severely  brought  to  book  for  suggesting  that 
where  holes  had  to  be  bored  by  machines  that  take  much  time 
to  set  up  and  adjust,  economy  in  drilling  and  in  explosives  would 
be  gained  by  drilling  long  holes  and  distributing  the  charge  into 
two  portions  by  interposing  tamping.  It  was  contended  that 


FIG.  136.  . 

such  a  practice  was  dangerous,  as  leading  to  unexploded  explosive 
being  left  in  holes,  and  in  any  case  to  defective  detonation. 

I  have  since  found  that  Gillette,  the  classical  authority  on 
such  matters,  recommends  the  same  thing  for  cutting  out  deep 
pipe  trenches.  By  inserting  a  primer  and  detonator  in  each  por- 
tion of  the  charge  objections  are  overcome,  and  in  this  way  alone 
can  long  holes  with  small  burdens  be  employed  in  narrow,  tight 
stopes.  If  interposed  tamping  is  used  without  any  separate 
means  of  detonating  the  lower  charge,  this  practice  is  open  to 
the  objections  urged  against  it,  and  detonation  by  concussion 
is  not  satisfactory.  Lower  grades  of  detonation  are  liable  to 


THEORY  OF  BLASTING  225 

result  in  waste  of  explosives  and  in  the  evolution  of  dangerous 
gases.  It  has  been  noted  already  that  even  in  a  single  charge 
3  ft.  long  in  a  bore  hole  the  bottom  cartridges  are  sometimes  not 
properly  detonated,  owing  to  their  distance  from  the  detonator. 
If  the  smaller,  one-man  drills  prove  unsuitable  for  work  in  narrow 
hard  stopes  having  a  dip  of  20  to  40  deg.,  and  should  ajabor 
shortage  be  met  with,  recourse  then  may  have  to  be  had  to  2|-in. 
or  2|-in.  machines  weighing  120  to  180  Ib.  for  narrow  stopes. 
These  can  be  employed  to  the  best  advantage,  boring  4  to  6  long 
holes  from  one  bench,  holes  being  5  to  7  ft.  long,  and  finished  off 
about  I!  in.  in  diameter.  In  these  the  charges  would  be  distrib- 
uted to  gain  economy  in  explosives.  Another  problem  connected 
with  mining  is,  what  is  the  right  diameter  to  finish  off  short 
machine  holes  in  small  stopes,  and  long  machine  holes  in  big 
stopes?  Is  the  idea  that  explosive  should  "be  where  it  belongs, 
at  the  bottom  of  the  hole,"  an  erroneous  one  in  working  most 
stopes,  as  the  authors,  I  believe  rightly,  say  it  is? 

If  the  length  of  charge  should  bear  a  definite  ratio  to  the 
length  of  hole,  then  the  length  of  charge  can  thus  be  best  increased 
by  decreasing  the  diameter  of  the  hole  within  limits.  The  larger 
we  bore  the  holes  with  machines  or  hand  drilling,  and  the  greater 
diameter  we  give  them  above  a  certain  right  amount  sufficient 
to  give  gas  enough  to  exert  proper  pressure  on  the  walls  of  the 
chamber,  the  more  time  and  money  we  waste  in  boring  the  holes 
and  in  the  amount  of  explosive  used.  This  amount  increases 
with  the  square  of  the  diameter  without  increasing  its  effective- 
ness at  a  like  ratio,  and  the  shorter  the  charges  we  get  in  our 
holes  the  more  we  must  limit  their  length  for  fear  that  "  bull- 
ringing"  will  be  caused. 


XII 
EXAMPLES  OF  ROCK  DRILL  PRACTICE 

SOUTH  AFRICA 

I  HAVE  endeavored  in  this  chapter  to  illustrate  by  examples 
drawn  for  actual  work  methods  of  breaking  ground  by  rock  drills 
on  the  various  mining  fields  of  the  world. 

Type  of  Rock.  —  The  rocks  in  the  lower  levels  of  Witwatersrand 
field  consist  of  quartzites,  grits,  and  conglomerates  with  slates  or 
shales.  Dikes  of  dolerite  are  encountered,  varying  in  hardness 
from  an  intensely  hard  diabase  to  the  soft  slaty  dikes,  so  decom- 
posed that  they  are,  when  interbedded,  hard  to  distinguish  from 
true  slates.  The  quartzites  and  conglomerates  vary  in  hardness; 
near  dikes  they  are  often  resilicified  and  sometimes  impregnated 
with  pyrite.  A  miner  who  knows  the  Cripple  Creek  district, 
Colorado,  well,  states  that  the  conglomerate  mined  in  South 
Africa  is,  on  an  average,  50  per  cent,  harder  than  the  granite 
and  phonolite  of  that  district.  As  a  rule,  the  rock  gives  little 
trouble  due  to  the  drill  bit  running  away  on  heads.  The  rock 
on  the  West  Rand  is,  however,  fairly  soft,  as  are  the  shales 
underlying  the  reef  in  the  eastern  portion. 

Dritts  in  Use.  —  The  standard  size  of  rock  drill  is  3 }  in.  diame- 
ter, with  stroke  from  5  to  7  in.  for  piston  machines.  These  are, 
however,  often  used  until  the  cylinder  has  been  rebored  to  3|  in. 
diameter.  For  stoping  a  few  2f-in.,  2J-in.,  2J-in.,  and  2-in.  piston 
machines  are  in  use;  but  the  question  as  to  the  type  of  machine 
suitable  for  small  stopes  has  not  yet  been  settled.  Experiments 
are  being  made  with  various  types  of  hammer  drills. 

The  makes  of  piston  drills  in  use,  at  present,  are  Ingersoll- 
Sergeant  auxiliary  valve;  Holman  Brothers'  auxiliary  valve; 
Stephens'  Climax  Imperial  air  valve;  Konomax  drill;  Tucking- 
mill  Foundry's  Little  Hercules  drill  (air  valve);  Ingersoll-Rand 
Slugger  and  Little  Giant,  with  a  few  experimental  drills. 

The  hammer  drills  in  use  in  1908  included  one  or  two  Leyner 

226 


EXAMPLES  OF  ROCK  DRILL  PRACTICE  227 

machines  and  some  Waugh  drills.  The  machines  that  have  been 
tried  here  include  Leyner,  Rock  Terrier,  Murphy,  Gordon,  Shaw, 
Little  Jap,  Little  Imp,  Hardscogg  Wonder,  and  others. 

Methods  of  Operation.  —  Drifting  is  generally  performed  with 
two  3j-in.  drills  mounted  on  arms  and  saddles  from  a  vertical 
bar.  This  work  is  performed  by  one  white  supervisor  and  four 
natives;  sometimes  another  young  native  is  needed  to  carry 
drills  and  water.  As  shown  below,  where  extra  rapid  progress 
is  required  three  machines  are  mounted  on  one  bar.  It  is  usual 
to  throw  the  dirt  back  from  the  face  before  starting  drilling; 
drifts  are  run  5  to  6  ft.  broad  and  about  7  ft.  high.  The  American 
practice  of  rigging  a  horizontal  bar  on  top  of  the  waste,  near  the 
roof,  and  starting  the  drill  at  once,  is  not  followed  because,  there 
being  more  labor  employed,  they  would  interfere  too  much  with 
one  another.  This  difference  in  practice  is  shown  by  comparing 
the  following  notes  on  driving  levels  with  that  on  American  tunnel 
practice.  The  contract  price  for  driving  in  quartzite  and  reef 
conglomerate  on  the  Rand  varies  from  25s,  or  $6,  to  40s,  or  $10 
per  foot,  according  to  the  hardness  of  the  ground  and  the  urgency 
of  the  work. 

The  contractor  would  pay  for  explosives  (blasting  gelatine 
being  usually  employed)  at  about  52s,  $13  per  case.  He  also 
pays  for  fuse,  candles,  detonators,  sometimes  oil,  blocks,  and 
wedges.  He  would  pay  his  natives  about  3s  each  per  10-hr, 
shift,  six  days  a  week.  In  certain  cases  one  white  contractor 
might  be  given  several  faces  to  work  and  more  than  two  machines 
to  supervise.  The  company  provides  compressed  air,  machines, 
hose,  spares  and  sharp  steel.  Sometimes  the  contractor  is 
allowed  a  certain  sum  per  month  for  repairs  to  machines  and  is 
charged  for  anything  in  excess  of  that  amount. 

Arrangement  of  Holes.  —  The  method  usually  employed  in 
arranging  the  holes  is  that  known  as  the  center  cut  method.  The 
drag  cut  is  seldom  or  never  employed.  The  reason  of  this  is 
again  found  in  the  class  of  labor  employed,  and  in  the  general 
necessity  to  do  rapid  development  work  in  order  to  keep  up  with 
the  demand  of  large  mills.  Hence  it  is  that  economy  in  time, 
rather  than  in  labor  and  explosives,  is  the  main  consideration. 

Where  the  reef  BC,  Fig.  137,  lies  very  steep  and  has  a  well- 
defined  parting,  or  head,  on  one  wall,  a  side  cut  as  shown  might 
be  drilled  to  the  head;  Nos.  1,  2,  3,  and  4  would  form  a  cut;  gen- 


228 


ROCK  DRILLS 


erally  3  would  be  omitted,  as  being  a  dry  hole  it  would  take  too 
long  to  drill.  These  would  be  fired  together .  An  ordinary  center 
cut  in  fairly  hard  ground  is  shown  on  the  following  pages,  using 
three  machines.  In  very  tight  ground  the  arrangement  shown 
in  Fig.  138  might  be  used;  Nos.  1,  2,  3,  4,  and  5  being  cut  holes, 
1  being  a  short  hole  18  in.  deep  to  break  the  collars  of  holes  6,  7, 
8,  9,  and  10;  these  are  easers  to  be  fired  after  the  cut;  12,  13,  and 

14  are  dry  holes  in  the  roof;   14  and  11  are  shoulder  holes,  while 

15  and  18  are  knee  holes;    16  and  17  are  lifters,  being  fired  last. 
In  easy  ground  the  arrangement  shown  in  Fig.  139  would  be  used; 


FIG.  137.  —  Arrangement  of  holes  on     FIG.  138.  —  Arrangement  of  holes  in 


steep  vein. 


'Tight"  ground. 


Nos.  1,  2,  and  3  being  cut  holes;  4  is  an  easer.  A  small  winze  or 
rise  would  be  advanced  with  from  7  to  12  holes,  arranged  as 
shown  in  Fig.  140. 

The  following  are  examples  of  work  done: 

Multiple  Arrangement  of  Drills.1  —  In  the  Cinderella  Deep 
mine  on  the  Rand,  in  the  Transvaal,  the  system  of  using  three 
machines  rigged  on  one  bar,  Fig.  141,  in  pushing  forward  an 
ordinary  7  X  5  ft.  drift,  was  introduced  by  Manager  Girdler 
Browne.  This  work  was  performed  at  a  depth  of  over  4000  ft. 
from  the  surface.  The  advance  was  225  ft.  in  a  month  of  31 

1  E.  M.  Weston,  Eng.  and  Min.  Journ,  Sept.  28,  1907. 


EXAMPLES   OF   ROCK   DRILL  PRACTICE 


229 


working  days.  Three  men  with  five  or  six  natives,  and  sometimes 
a  white  assistant,  worked  in  8-hour  shifts.  Compressed  air  was 
freely  used  for  blowing  out  the 
smoke,  and  the  rock  was  wetted 
after  a  blast.  As  soon  as  the  rock 
was  sufficiently  shoveled  back  from 
the  face,  the  miners  returned,  set 
up  the  drills  and  started  drilling, 
while  the  rest  of  the  rock  was 
being  moved.  The  rock  had  to 
be  trammed  500  to  800  ft.  The 
best  previous  drifting  record  was 
in  the  Roo deport  district,  in  soft 
ground  requiring  only  9  holes  per 
round.  The  distance  driven  was 
220  ft.  in  one  month.  On  the 
Cinderella  Deep  the  quartzites  FlG-  139-  ~  Arrangement  of  holes 
forming  the  hanging  wall  of  the 

banket  reef  are  very  hard.  The  reef  itself  is  of  moderate  hard- 
ness and  the  dark  quartzite  or  quartzose  slates  under  the  reef 
are  usually  fairly  soft.  The  illustrations  show  a  normal  face 
bored  out  with  15  holes.  Where  the  drive  gets  more  into  the 
hanging  wall,  more  holes  may  be  required.  Four  or  five  holes 
may  be  necessary  on  either  side,  and  perhaps  other  easers.  The 
bar,  which  is  usually  a  " double-jack"  bar,  is  rigged  as  securely 
as  possible  about  4  ft.  from  the  face.  One  arm  is  rigged  as 
shown,  to  put  in  a  flat  hole  in  the  hanging  wall;  another  is 

fixed  directly  below  this  to  bore 
the  roof  hole  on  the  other  side  of 
the  drive.  Safety  clamps  are  put 
on  under  these  two  arms  and  also 
under  the  bottom  arms.  The  third 
arm  is  rigged  lower  doAvn  to  bore 
the  top  hole  of  a  three-hole  cut. 
This  is  generally  put  in  to  take 
advantage  of  the  contact  between 
reef  and  foot-wall.  The  two  dry 
holes  and  the  cut  hole  are  first 
slated  and  then  the  holes  of  the  face  are  bored  in  the  rota- 
tion shown  by  the  numbers  on  the  drawing.  The  top  ma- 


FIG.  140.  —  Plan  of  holes  in  bot- 
tom of  winz. 


230 


ROCK   DRILLS 


EXAMPLES  OF  ROCK   DRILL  PRACTICE  231 

chines  drill  the  shoulder  holes,  Nos.  4  and  5,  without  altering 
the  arms. 

No.  1  machine  drills  holes  1,  4,  7,  10.  No.  2  machine  drills 
holes  2,  5,  8,  11,  13.  No.  3  machine  drills  holes  3,  6,  9,  12,  14,  15. 

Though  No.  1  machine  has  only  four  holes  to  drill,  the  flat 
hole  in  the  hanging  wall  takes  so  long  that  it  is  not  finished  much 
before  the  others;  the  No.  2  machine  has  all  water  holes  to  bore 
and  should  be  rigged  under  the  arm  drilling  the  lifter  holes  14 
and  15  before  No.  2  machine  comes  down  to  drill  hole  2.  No.  2 
machine  has  hole  13  to  drill  after  No.  1  has  drilled  hole  10.  If 
possible  No.  1  machine  is  not  given  more  to  do  after  it  has 
bored  hole  10  as  it  is  almost  impossible  to  work  with  all  the 
arms  low  down  on  bar.  Very  often  when  the  foot-wall  ground 
is  soft,  No.  3  finishes  first  and  it  can  then  be  used  to  collar 
holes  for  the  other  machines.  In  the  same  way  Nos.  1  and 
2  machines  can  cross-collar  difficult  holes  for  each  other. 
Four  or  more  IJ-in.  sticks  of  blasting  gelatine  are  placed  in 
each  cut  hole  and  from  five  to  six  in  the  other  holes.  The 
cut  is  blasted  first,  then  the  easers,  then  the  shoulder  and  knee 
holes,  then  the  back  holes,  and  lastly  the  lifters.  No.  8  hole 
is  run  in  under  the  contact  of  reef  and  foot-wall  to  prevent 
any  lump  being  left  on  the  side  of  the  drift. 

The  drift  is  run  at  a  grade  of  one  in  150  to  200  and  has  a 
single  track  with  sidings  every  few  hundred  feet.  For  a  long 
drive  the  drift  is  squared  off  by  hand  labor  to  allow  of  a  venti- 
lating pipe  being  laid  along  the  track.  The  air  pressure  em- 
ployed in  the  Cinderella  Deep  was  about  80  Ib.  per  square  inch. 
Machines  with  3  J-in.  cylinders,  made  by  Holman  &  Son,  Cornwall, 
England,  were  employed.  Star-section  welded  steel  bits,  up  to 
5-ft.  lengths,  and  longer  lengths  of  chisels  (up  to  7  ft.)  were 
employed.  The  diameter  of  starter  bits  was  from  2f  in.  to  3 
in.  and  the  difference  in  gage  about  0.25  in.  The  finishing  bit 
was  If  in. 

Record  Driving  in  the  Rand  Deep  Levels.  —  On  the  Simmer 
Deep,  which  is  about  4000  ft.  deep,  the  fifteenth  level  was  advanced 
294  ft.  in  61  shifts  of  10  hours.  The  size  of  the  drive  along  the 
reef  and  through  dike  was  7  X  5  ft.  One  white  man  and  six 
Chinese  operated  three  Ingersoll-Sergeant  3J-in.  drills  on  one 
bar.  One  round  was  drilled  and  blasted  each  shift,  and  the 
average  gains  per  round  was  4.8  ft.  Blasting  gelatine  was 


232    .  ROCK  DRILLS 

employed,  and  50  Ib.  were  used  to  advance  4.5  ft.  or  11  Ib.  per  foot. 
Fifty-nine  of  the  rounds  needed  14  holes  with  the  usual  three- 
hole  center  cut  to  break  them;  100  rounds  required  only  12  holes. 
The  air  pressure  at  the  surface  was  80  Ib.,  and  owing  to  the  pres- 
sure gained  at  such  great  depths  due  to  the  difference  in  weight  of 
a  column  of  dense  air  compressed  to  80  Ib.  in  the  pipes  and  the 
normal  air  in  the  main  pipe,  friction  was  balanced  and  the  air 
was  supplied  to  the  machines  themselves  at  80  Ib.  This  gain 
in  air  pressure  at  about  4000  ft.  equals  10  Ib.  per  square  inch. 
Water  was  laid  on,  and  an  arrangement  was  also  made  whereby 
the  water  could  be  turned  into  the  air  pipe,  making  a  spray  after 
blasting  and  at  once  cooling  the  drive  and  laying  the  dust. 

In  comparing  these  results  with  those  gained  in  adit  driving 
in  America,  it  must  be  borne  in  mind  that  these  drives  are  not 
straight,  that  mechanical  haulage  is  not  used  and  that  the  ground 
is  generally  harder  and  requires  more  holes  and  larger  quantities 
of  more  powerful  explosives,  while  the  smaller  size  of  the  excava- 
tion does  not  give  room  for  an  economical  arrangement  of  holes. 

Truscott  states  that  on  the  eighth  level  of  the  Durban 
Roodeport,  a  drive  was  advanced  225  ft.  in  one  month.  The 
size  of  drift  was  C  X  5J  ft.  Two  rounds  were  fired  daily, 
breaking  from  3  to  4  ft.  of  ground.  Only  eleven  holes  were 
drilled  in  face. 

At  the  Van  Dyke  mines  two  men  with  two  machines  drove 
227  ft.  in  one  month  in  shale  and  quartzite  working  alternate 
lOj-hour  shifts.  The  consumption  of  explosives  varied  from 
40  to  75  Ib.  per  round.  Where  a  round  of  4|  to  5  ft.  is  taken  out 
by  holes  from  5  to  6  ft.  long,  the  consumption  of  explosive  in  a 
drive  6  X  7  ft.  is  about  3  Ib.  per  ton,  when  50  Ib.  of  explosives 
are  used.  The  charge  for  the  three  cut  holes  each  is  generally 
5  to  7  sticks  of  blasting  gelatine,  1J  in.  X  7  in.  The  other  holes 
having  a  burden  of  30  to  36  in.  require  5  sticks  each. 

A  drive  was  advanced  on  the  East  Rand  Extension  a  distance 
of  361  ft.  in  one  month.  Ingersoll-Sergeant  3i  in.  machines 
were  used,  working  three  shifts  per  day.  The  average  number 
of  holes  was  12.7  per  round.  The  average  distance  of  the  breast 
from  the  shaft  was  over  half  a  mile,  and  all  the  broken  ground 
and  supplies  had  to  be  transported  this  distance. 

During  September  in  the  Modderfontein  "B"  Gold  mines 
a  drive  was  advanced  334  ft.  Two  machine  men,  one  trammer, 


EXAMPLES   OF   ROCK   DRILL   PRACTICE 


233 


and  two  Ingersoll-Sergeant  machines  were  employed.  Shifts, 
62.  Average  holes  per  round,  12.5;  average  footage  per  day, 
11.13  ft.;  size  of  drive,  6  ft.  by  7  ft. 

In  July  349  ft.  were  accomplished  at  the  New  Modderfontein, 
but  this  was  in  two  faces.  Against  this  the  work  was  only  single 
shift  as  compared  with  double  shift  at  the  Modderfontein  "B." 

The  previous  good  result  is  305  ft.,  accomplished  about  three 
months  back  at  the  Vogelstruis  Consolidated  Deep. 

At  the  New  Modderfontein,  on  the  seventh  level  of  No.  12 
shaft,  Messrs.  Corris  and  McHendry  drove  during  May  267  ft., 
June  264  ft.,  and  July  295  ft.,  —  a  total  of  826  ft.  for  156  consecu- 
tive shifts.  This  is  claimed  to  be  the  record  for  consecutive 
working. 

Mr.  J.  P.  Ward,  in  Journ.  Chem.  Met.  and  Min.  Soc.,  recom- 
mends the  following  arrangement  of  cut  holes  (Fig.  142),  and 


FIG.  142.  —  Arrangement  of  cut  holes. 

states  that  he  found  it  most  satisfactory  to  so  distribute  the 
powder  as  to  give  the  cut  itself  something  to  break  to.  The 
accompanying  figure  illustrates  the  idea.  The  cut  is  drilled  as 
usual,  holes  18  in.  apart,  and  running  to  be  all  within  a  6-in. 
circle  at  the  back.  The  two  longest  holes,  in  this  case,  1  and  2, 
are  charged  with  four  plugs  of  IJ-in.  gelatine  each,  and  well 
tamped,  no  fuse  being  used;  the  third  hole  is  charged,  two  plugs, 
then  tamping,  two  plugs,  tamping,  two  plugs  and  primer;  the 
latter  is  now  not  more  than  18  in.  from  the  face  and  is  well 
tamped.  A  fuse  is  inserted  in  the  third  hole  only,  to  ensure 
this  going  first,  its  duties  being  to  smash  the  face  and  detonate 
Nos.  1  and  2. 

Channeling  Cut.  —  Three  holes  are  drilled  in  the  face  the  de- 
sired depth.  They  are  put  in  horizontally,  Fig.  143,  the  three 
being  in  a  vertical  plane,  one  above  the  other,  4  to  6  in.  apart,  and 


234 


ROCK  DRILLS 


fired  as  follows:  The  middle  hole  is  not  charged  but  left  empty, 
the  top  and  bottom  holes  are  charged  and  fired  one  after  the  other; 
it  makes  a  gap  about  15  to  18  in.  high  and  the  width  of  the  hole; 
it  takes  less  explosive  and  any  practical  length  of  cut  can  be 
broken,  for  so  long  as  the  holes  are  parallel  the  cut  can  be  broken. 
If  cuts  of  good  length  can  be  brought  out,  longer  rounds  can  be 
broken  with  the  same  amount  of  explosive  than  most  miners  use 
for  the  shorter  rounds,  therefore  the  cost  per  foot  will  be  less. 
This  cut  would  be  suitable  for  soft  ground  only. 

Differences  in  Miners.  —  The  art  of  driving  is  to  arrange  the 
holes  in  such  a  way  and  drill  a  sufficient  number  to  a  depth  that 
the  maximum  advance  will  be  made  with  one  set-up  of  the 
machine  where  large  piston  drills  are  used.  Most  miners  tend  to 


FIG.  143.  —  Channeling  cut. 

put  in  too  few  holes,  hence  unblasted  stumps  up  to  12  or  18  in. 
long  may  be  left  out  of  a  total  of  60  or  72  in.  In  supervising 
development  work  in  a  mine  where  numerous  faces  are  at  work, 
it  is  always  advisable  at  the  end  of  a  month  to  divide  the  total 
footage  driven  in  any  heading  by  the  number  of  blasts  made. 
The  result  gives  the  linear  advance  per  round  and  the  difference 
in  the  work  of  various  men  is  at  once  shown. 

Size  of  Drill  Steel.  —  This  varies  on  different  mines;  generally 
the  same  steel  is  used  for  development  and  for  stoping.  The 
size  of  bits  used  on  Meyer  &  Charlton  mine,  1908,  was: 


1st,  star  bit,  24  in.  long,  diameter,  2|  in. 
2d,  star  bit,  39  in.  long,  diameter,  2J  in. 
3d,  star  bit,  60  in.  long,  diameter,  If  in. 
4th,  star  bit,  84  in.  long,  diameter,  1J  in. 


(Starter.) 


Transcott  gives  usual  sizes  as, 
1st,    cross-bit,    24    in.   long, 

diameter,  3  in.      (Starter.) 
2d,    cross-bit,    39    in.    long, 

diameter,  2J  in. 
3d,    chisel   bit,   57  in.  long, 

diameter,  1  j  in. 
4th,  chisel  bit,  84  in.  long, 

diameter,  If  in. 

Another  mine  used, 

1st,    star   bit,    30   in.    long, 

diameter,  2f  in.    (Starter.) 
2d,    star    bit,   48    in.    long, 

diameter,  2J  in. 
3d,    star    bit,    66    in.    long, 

diameter,  2  in. 
4th,    chisel  bit,  72  in.  long, 

diameter,  If  in. 

These  are  for  development  work, 
while  longer  chisel  bits  are  some- 
times used  for  stoping. 

As  before  remarked,  the  gage 
of  the  bits  is  determined  by  the 
greater  wear  in  putting  in  dry  flat 
holes,  separate  steel  not  being  used 
for  this  work. 

SHAFT  SINKING  AS  PRACTISED  ON 
THE  RAND 

The  favorite  method  has  been 
the  single  jack  and  hand  labor,  but 
machines  are  also  used  in  both  ver- 
tical and  inclined  shafts.  The  fol- 
lowing are  particulars  of  sinking 
two  vertical  shafts  on  the  Rand 
Collieries,  Ltd.: 

Character  of  Rock.  — Bore  holes 
had  shown  that  the  ground  to  be 
sunk  through  on  this  property,  see 
Fig.  144,  was  largely  composed  of 
interbedded  diabase  sheets.  The 


Clay 
lual 

Dwyka  UUciul 


Hard  Quartzite*  Jt 
Conglomerates  uf 
KlmU-r.ly  Series 


WeWinorphosi-.rSlad-  and  __ 

Decomposed  Diabase  lull  »t  £ 

Dangerous  slips  and  heads  vr/  CS 

hard  Pq 


Diabase  showing  Scrpmitliil/.alton 
foil  of  dangerous  (dips  and  l»sul* 
Decomposed  Diabase 


Interbedded  Diabase 
Quartz  ite 
Diabase 

Diabu *  Dike 


Amygdaloklal  Diabase 
Hard  QuarUite 
Amyt'daloidal  Diabase 
Hard  Quaitzlte 

Conglomerates  &  Qiwi  uites  wf 
Bird  Reef  Series 


QuartzitM 

Uiubiwe 

Onanzilet 

Diabase 

Quiuuites 

Diabase 

QuaiUitel 
Main  Reef 


236 


ROCK  DRILLS 


largest  one,  occurring  in  the  middle  of  Kimberly  slates,  was  of 
exceptional  hardness  and  toughness,  consisting  in  its  core  of  a  fine- 
grained aggregate  of  pyroxene  and  labradorite  crystals.  The  other 
diabase  sheets  were  of  varying  hardness,  being  somewhat  decom- 
posed, but  these  sheets  had  all  re-silicified  the  quartzites  in  their 
immediate  neighborhood,  rendering  them  much  harder  than  the 


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FIG.  145.  —  Section  and  plan  No.  1  Shaft  Rand  Collieries,  Ltd.,  showing  posi- 
tion of  drilling  bars  and  arrangement  of  drill  holes. 

average.  G.  A.  Denny,  the  consulting  engineer  to  this  company, 
owing  to  the  character  of  the  ground  disclosed,  decided  to  use 
machines  for  sinking. 

Routine  of  Shaft  Sinking  with  Machines.  —  The  routine  of 
shaft  sinking  with  machines,  at  the  Rand  Collieries,  Ltd.,  Fig. 
145,  is  as  follows.  Three  white  men  work  8-hr,  shifts  and  super- 
vise the  cleaning  out  of  the  shaft  and  help  during  the  drilling 


EXAMPLES   OF  ROCK  DRILL  PRACTICE  237 

shift.  These  are  paid  £1  per  shift.  Three  whites  and  a  foreman 
and  about  25  natives  or  Chinese  comprise  the  drilling  crew. 
There  are  three  shifts  of  shovelers.  These  go  down  in  rotation 
after  a  blast;  their  task  is  to  send  up  60  buckets  of  rock,  or,  when 
the  bottom  has  to  be  scraped,  only  50  buckets.  There  are  about 
25  natives  or  Chinese  on  each  of  these  mucking  shifts.  The  white 
men  on  the  drilling  crew  get  25s.,  or  $6,  per  day.  They  have  to  do 
the  drilling  and  they  also  have  to  go  down,  when  required,  to 
assist  in  blowing  out  holes  for  second  blasting  and  to  help  clean 
down  the  timbers  and  to  lower  hose  ready  for  the  drilling  shift. 
Natives  and  Chinese  get  2s.  per  shift  with  a  6d.  or  Is.  bonus  for 
work  performed  within  a  specified  time.  A  bonus,  depending  on  the 
equipment  of  the  shaft  and  the  class  of  ground  passed  through,  is 
also  given  for  feet  sunk  greater  than  a  certain  footage  per  month. 

As  soon  as  the  ends  of  the  shaft  are  cleaned  up,  blocks,  wedges, 
and  bars  are  sent  down  and  the  end  bars  rigged  up.  Hose  are 
lowered  and  any  defective  ones  replaced;  any  stumps  of  holes  are 
blown  out  and  plugged.  Then,  when  the  center  of  the  shaft  is 
cleaned  out,  the  drilling  crew  come  down  and  work  is  started. 

Where  the  ground  is  shattered  by  joint  planes  or  by  previous 
blasts,  but  not  broken  sufficiently  to  remove,  or  where  drilling 
has  to  go  on  under  water  so  that  there  is  a  danger  that  rock  frag- 
ments will  wash  into  the  holes,  collar  pipes  are  driven  into  the 
mouth  of  the  hole.  These  are  pieces  of  old  pipe  or  boiler  tube 
about  12  in.  long,  having  a  3-in.  to  3j-in.  diameter  inside.  These 
help  the  drilling  greatly,  for  the  hole  "muds"  better  than  when 
drilling  under  water,  for  it  can  splash  when  these  are  used.  After 
the  hole  is  loaded,  when  it  is  possible,  these  pipes  are  drawn  so 
as  to  be  used  again.  When  the  ground  is  of  such  a  character 
that  the  mud  tends  to  settle  in  the  bottom  of  the  hole,  the  mud 
is  pumped  out,  whenever  a  drill  is  changed.  For  this  purpose, 
pipes,  3  to  12  ft.  long  and  from  f  to  2  in.  diameter,  are  used.  They 
are  moved  rapidly  up  and  down  in  the  hole  while  the  hand  is 
used  as  a  valve  at  the  top  of  the  pipe.  The  pipe  is  kept  closed 
on  the  up  stroke  and  the  hand  is  taken  away  on  the  more  rapid 
down  stroke.  This  throws  the  mud  and  water  out.  In  other 
places  elaborate  pumps,  made  with  a  plunger  and  a  marble,  or 
other  valve  at  the  bottom,  are  employed.  Ordinary  blow-pipes 
are  also  used  here,  but  only  when  coarse  grit  or  rocks  in  the  holes 
render  their  use  necessary. 


238  ROCK  DRILLS 

A  single  snatch-block  is  hung  from  the  lowest  set  of  timbers 
and  a  rope  and  hook  are  used  to  hoist  the  machines  in  and  out 
of  the  buckets  and  to  swing  them  into  position  in  any  part  of 
the  shaft.  The  machines  are  rigged  on  clamps  directly  off  the 
bars,  which  are  8  ft.  long  and  4J  in.  diameter.  There  is  no  diffi- 
culty in  making  a  secure  set-up.  Occasionally  the  bars  have 
to  support  four  machines  at  work,  but  generally  two  are  placed 
on  each  bar  except  the  one  on  the  pump  end  which  carries  three. 

Machine  Drilling  in  Hard  Rock.  —  The  drilling  of  long  holes 
in  the  shaft  bottom,  when  the  ground  is  full  of  joints  and  slips, 
requires  considerable  skill.  In  hard  ground  a  close  watch  has 
to  be  kept,  so  that  drills  are  not  kept  at  work  after  they  are  too 
dull,  otherwise  the  drills  will  either  bend  or  break,  or  else  it  will 
be  found  impossible  to  get  the  next  drill  to  follow.  Realining  a 
drill  in  a  hole,  that  has  "run  away,"  is  not  so  easy  as  it  is  when 
an  arm  is  used  on  the  bar,  for  no  change  in  vertical  elevation  can 
be  made.  If  a  hole  gives  trouble  the  jig  bolt  is  first  slackened  a 
little,  then  the  clamp  is  removed  along  the  bar,  in  whatever 
direction  may  appear  best,  and  the  bolts  tightened  again.  If 
trouble  is  still  apparent  the  clamp  bolts  are  loosened  a  little, 
while  the  machine  is  running;  then  very  often  the  machine  will 
aline  itself.  The  following  trick,  used  when  a  bit  is  slightly  too 
large  for  the  hole,  is  certainly  bad  practice;  but  nevertheless,  it  is 
often  useful.  The  chuck  bolts  are  loosened  and  the  machine  is 
cranked  back  so  that  the  chuck  is  used  as  a  hammer  to  strike  the 
shank  of  the  drill;  meanwhile  the  drill  is  turned  by  hand.  The 
hole  can  thus  often  be  reamed  out  and  the  drill  made  to  follow. 

As  we  had  no  drill-sharpening  machine  at  this  mine,  bits 
of  star  section  could  not  be  jumped  up  and  formed  from  the  steel. 
Consequently  we  had  to  follow  what  is  the  usual  custom  in  this 
field  of  using,  for  all  cross-bits,  star-section  steel  welded  upon 
octagon  steel.  There  are  in  fact  only  a  few  mines  on  the  Rand 
equipped  with  machines  for  sharpening  and  making  machine 
drill  bits.  In  this  respect  I  believe  American  practice  is  far  in 
advance  of  ours,  when  really  hard  ground  has  to  be  drilled.  Welds, 
however  well  made,  are  always  a  source  of  weakness  and  trouble. 

The  diabase  in  this  shaft  was  of  exceptionally  hard  and  tough 
character.  Therefore  during  the  drilling  shift,  it  was  necessary 
to  have  a  blacksmith  always  available  to  sharpen  drills  to  any 
gage  required  owing  to  bits  wearing  abnormally  or  shattering. 


EXAMPLES   OF   ROCK   DRILL  PRACTICE 


239 


Star  bits  had  to  be  employed  up  to  a  length  of  7|  ft.,  as  chisel 
bits  lost  their  gage  too  rapidly.  At  the  Village  Deep  shaft,  where 
the  rock  was  favorable  for  drilling,  only  chisel  bits  were  used, 
after  the  starter  had  " pitched"  the  hole. 

Recovering  Broken-off  Bits.  —  Owing    to   the   use   of  welded 
steel,  breakage  of  drills  was  frequent  and  holes  were  repeatedly 


FIG.  145a.  —  Arrangement  of  bell  crank  levers, 
used  in  signaling,  Rand  Collieries. 


FIG.  146.  —  Clamps  used  to  extract  drills  from 
fitchered  holes. 

lost  owing  to  this  cause.  Nothing  is  more  annoying  and  dis- 
heartening to  the  operator  than  to  have  a  6-in.  end  break  off  in  a 
5-ft.  hole  that  had  required,  as  was  frequently  the  case,  three 
hours'  drilling  to  reach  that  depth.  I  found  it  impossible  to  devise 
any  really  satisfactory  tongs  or  other  extractor  for  regaining  these 
ends.  When  drills  stuck  in  holes,  owing  to  bending  or  other 
causes,  I  found  a  clamp  extractor,  Fig.  146,  very  useful. 


240 


ROCK   DRILLS 


The  air  pressure  that  we  used  in  hard  rock  was  80  Ib.  per 
square  inch;  when,  in  the  hardest  rock,  we  found  it  better  to 
reduce  this  to  70  Ib.,  for  though  the  speed  of  drilling  was  much 
reduced,  fewer  drills  were  broken  and  fewer  holes  were  lost  on 
that  account.  But,  when  the  shaft  bottom  was  in  quartzites  of 
moderate  hardness,  90-lb.  pressure  was  employed  and  it  resulted 
in  much  more  rapid  drilling.  In  such  rock  three  8  ft.  vertical 
holes  are  easily  drilled  in  two  hours;  at  the  producing  mines 
in  rock  of  the  same  hardness,  with  the  low-air  pressure  there 
employed,  22  ft.  of  hole  is  the  average  amount  drilled  during 
an  8-hr,  shift. 

Size  of  Steel   Used.  —  Only  the  best  brands  of   chisel   steel 


V  u  J 


FIG.  147.  —  Simplex  drill  chuck. 

costing  11  to  12  cents  per  pound,  would  stand  in  this  diabase 
without  bending;  but,  for  the  longest  drills,  having  chisel  bits 
and  11  ft.  long,  1-in.  steel  was  found  to  stand  satisfactorily  with 
the  3J-in.  machines.  Next  to  the  welds,  the  worst  breakage  of 
steel  occurred  at  the  shanks.  The  ends  of  the  shanks  were 
most  carefully  hardened  to  prevent  burring  up,  but  they  broke 
badly  just  outside  the  chuck,  where  the  diameter  was  reduced  by 
swaging  to  form  the  shank. 

In  the  patent  Simplex  chuck,  Fig.  147,  manufactured  by 
Stephens,  of  Camborne,  England,  steel  of  ordinary  octagonal 
section  can  be  used  without  shanking.  As  shown  in  the  accom- 
panying cut,  the  side  of  the  chuck  is  cut  away  and  the  long  pad 
or  key  clamps  the  steel  against  a  half-chuck  bushing  on  the  other 


EXAMPLES   OF   ROCK   DRILL   PRACTICE 


241 


side.  Wear  on  this  bushing  can  be  cheaply  taken  up  by  liners. 
The  key  is  easily  tightened  or  loosened  by  a  tap  of  a  hammer. 
A  great  saving  in  bushings  and  in  the  cost  of  shanking  results 
when  this  chuck  is  used. 

The  machines  in  use  here  are  3-J-in.  Ingersoll-Sergeant  drills, 
equipped  with  an  auxiliary  valve,  and  the  3J-in.  Holmarr  air- 
valve  drills.  No  great  difference  in  the  speed  of  drilling  was  noted. 
Eleven  machines  are  used  in  the  shaft  bottom.  At  the  Village 
Deep  shaft  12  machines,  rigged  on  four  bars,  were  used.  Here 
we  sometimes  find  11  machines  sufficient,  but  often  12  were 
used.  The  hoisting  buckets  work  in  the  two  compartments,  5  ft. 
long,  next  the  pump  compartment.  The  pump  compartment 


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FIG.  148.  —  Arrangement  of  four  drill  bars  in  bottom  of  shaft. 

is  8  ft.  long.  When  the  sump  or  cut  is  taken  out  under  the  two 
hoisting  compartments  there  is  a  space  of  about  13  ft.  at  one  end 
of  the  shaft  and  10  ft.  under  the  pump-compartment  end.  Five 
bars  are  rigged,  two  under  the  pump  end  and  three  under  the  two 
unused  hoisting  compartments.  Five  machines  drill  15  holes 
on  one  side  of  the  cut  and  six  machines  drill  18  holes  on  the  other 
side  of  the  cut.  If  any  extra  holes  should  be  required,  there  is 
always  a  machine  that  has  finished  its  holes,  before  the  machines, 
drilling  the  center  cut  holes,  are  through,  and  it  is  available  for 
the  work.  The  distances  between  the  bars  and  the  arrangement 
of  holes  are  shown  in  Fig.  148. 

METHOD  OF  HANDLING  THE  AIR  HOSE 

The  air  is  carried  down  the  shaft  in  a  6-in.  pipe,  placed  in 
the  pump  compartment.  A  double  platform  is  put  in  over  the 
pump  compartment  and  the  two  unused  hoisting  compartments. 


242  ROCK  DRILLS 

LOG  FOR  SHAFT  SINKING  WITH  MACHINES,  RAND  COLLIERIES,  LTD. 


December,  1906 

Buckets 
Hoisted 

Time  of  Shift 

Length 
Shift 

Time  Lost 

Date 

Shift 

i 

1 

03 

Timber 
Cleaning 

M 

.S-8 

III 

| 

1 
ffl 

5th 

Drilling 



6 

1:40  a.m.    4:10  a.m. 

Hr.    M. 
14     30 

Hr.  M. 
1      25 

Hr.  M. 

Hr.  M. 

— 

Mucking  1st 

60 

— 

5:35  a.m.  10:10  a.m. 

4     35 

— 

1      35 

— 

6th 

2d 

50 

— 

11:  45  a.m.    3:  20  p.m. 

3     35 

— 

— 

— 

— 

3d 

50 

— 

3:  20  p.m.  11:45  a.m. 

5     55 

— 

— 

1     30 

7th 

4th 

20 

— 

12:  15  a.m.    3:45  a.m. 

3     30 

— 

— 

— 

Total  buckets! 
hoisted       j 

180 

— 

Total  time  j 
mucking    j 

17     35 

1     25 

1     35 

1     30 

Total  time  for  round  =  36  hr.  35  min. 

Footage  sunk  for  week  =  28  ft.     For  month  =  103  ft. 

Ground  sunk  through,  hard  diabase. 

Number  of  machines  drilling  on  shaft  bottom,  11. 


A  cross  piece  of  4-in.  pipe,  provided  with  cocks,  is  run  across  the 
shaft;  five  hose  are  coiled  on  hooks,  hanging  from  the  shaft 
timbers  on  one  end  and  the  other  six  on  the  other  end.  At  first 
these  hose  were  100  ft.  long  and  the  stage  kept  from  60  to  100  ft. 
from  the  bottom,  the  6-in.  pipe  being  lengthened  whenever  a 
distance  of  40  ft.  was  sunk.  In  really  hard  ground,  however, 
the  hose  and  platforms  suffered  too  much  from  flying  rock.  Hose, 
150  ft.  long,  were  therefore  used  and  the  platforms  kept  further 
from  the  bottom.  Six  natives  and  a  white  man  are  sent  up,  just 
before  the  drilling  of  the  round  is  completed,  to  haul  up  the  hose. 
Two  of  the  natives  remain  on  the  timber  platform  about  40  ft. 
from  the  shaft  bottom;  thus  the  hose,  though  heavy,  are  easily 
and  quickly  hauled  up. 

In  some  cases  all  the  hose  are  attached  to  one  detachable  pipe 
and  are  counterbalanced  by  a  weight  on  a  rope  passing  over  a 
pulley  up  in  the  shaft.  This  pipe  is  taken  off  just  before  blast- 
ing and  hoisted  high  enough  so  that  the  hose  hang  high  enough 
in  the  shaft  to  be  out  of  the  way  of  flying  rocks.  This  method 
has  the  disadvantage  that  excess  length  lowered  must  be  taken 
up  again  and  the  hose  secured  with  rope;  besides,  all  the  hose 


EXAMPLES  OF  ROCK   DRILL  PRACTICE  243 

must  be  lowered,  when  only  one  is  required  at  each  end  of  the  shaft 
for  blowing  out  holes,  etc.;  the  remainder  are  then  in  the  way 
of  timbering  and  shoveling.  The  platform  method,  though  it 
is  expensive  and  troublesome,  is  perhaps  the  most  convenient. 
The  costs  of  sinking  these  shafts  during  certain  months,  are 
shown  in  accompanying  tables: 

COST  OF  SINKING  No.  1  SHAFT 

August,  1907;  131  ft.,  sunk  through  hard  quartzites 

£         s.  d. 

Winding  ropes  and  bell  lines 11.183 

Tramming 17  7.611 

Sinking l 7         14  1.923 

Cleaning  up  broken  rock 4          0  0.672 

Pumping 1          2  2.885 

Hauling 1         13  11.527 

Lighting : . _6^  6.336 

Total  sinking  costs  per  foot 15         15  6.137 

Timbering 4         17  5.315 

Ladders 2  5.413 

Lagging 6  9.020 

Air  brattice 7  0.375 

Total  cost ....  ^l        ~0  10.0 

General  expenses  on  two-shaft  basis    1           5  9.8 


Total  cost  per  foot 22          6  7.8 

1  This  includes  the  cost  of  breaking  the  ground  and  shoveling,  of  explo- 
sives and  of  maintenance  of  rock  drills. 

COST  OF  SINKING  No.  11  SHAFT 

December,  1906,  103  ft.,  sunk  through  hard  diabase 

£         s.  d. 

Winding  ropes  and  bell  lines 7  4.1 

Surface  tramming 1           2  4.5 

Sinking l 14           9  8.0 

Pumping 1           7  2.2 

Hauling 2          0  7.2 

Lighting    —          3  3.8 


Total  sinking  costs  19         12  6.31 

Timbering 4         19  7.31 

Ladders     2  10.67 

Air  brattice  wall 6  11.23 

Lagging 19  7.29 

Administration  and  general  charges 2           1  2.40 

Total  cost  per  foot   28          2  9.21 

1  This  includes  the  cost  of  breaking  the  ground  and  shoveling,  of  explo- 
sives and  of  maintenance  of  rock  drills. 


244  ROCK  DRILLS 


SUMP  AND  BENCH  SYSTEM 

The  Cinderella  Deep  shaft  was  sunk  by  this  system;  the 
advantage  claimed  for  the  method  is  economy  in  labor  and  explo- 
sives. Mr.  G.  Browne  gives  the  following  particulars  in  regard 
to  sinking  this  shaft.  The  shaft  was  excavated  9  X  32  ft. 

"When  sinking  with  four  machines,  three  men  are  employed, 
one  being  responsible  for  placing  the  holes.  Two  bars  are  used, 
with  two  machines  on  each  bar,  so  that  each  man  has  two  machines. 
The  leading  hand  relieves  and  helps  throughout  the  shift;  he 
also  looks  after  the  hand-drill  labor.  With  this  method  a  number 
of  hand-drill  boys  (natives),  not  exceeding  ten,  are  put  to  work 
drilling  holes  for  shaping  the  shaft  and  easing  sockets  which  had 
not  broken  to  the  bottom  on  the  previous  blast.  Two  boys  are 
allowed  to  each  machine. 

"The  scheme  of  drilling  calls  for  the  taking  up  of  the  sump 
on  the  one  shift  and  the  benches  during  the  next.  The  time  taken 
to  drill  over,  from  the  tirrie  the  men  leave  the  bank  until  blasting- 
takes  place,  averages  8J  hours.  The  sump  is  usually  blasted  with 
16  to  18  holes.  The  lifting  sump  holes  are  finished  off  with  a 
special  long  chisel  jumper  10  ft.  in  length.  The  back  holes  (ver- 
tical) are  drilled  to  a  depth  of  8  ft.  Great  care  is  taken  that 
jumpers  are  not  allowed  to  wear  short. 

"  Mucking.  —  Immediately  after  blasting  the  cleaner  goes 
down,  spending  on  an  average  If  hours  in  cleaning  down  the  bot- 
tom two  sets  of  timbers,  and  in  an  examination  of  the  sides  of  the 
shaft  from  the  last  set  of  timbers  (usually  kept  between  50  and 
60  ft.  from  the  bottom).  Following  upon  this,  25  to  30  cleaning 
boys  are  sent  down,  arid  the  first  bucket  of  rock  is  up  within 
two  hours  from  the  time  of  blasting.  The  average  number  of 
buckets  of  rock  obtained  from  a  sump  blast  is  110,  and  the 
average  time  to  clean  out  the  shaft  bottom  is  18  hours. 
After  the  first  65  buckets  are  sent  up,  the  shift  of  cleaners 
is  changed,  the  second  shift  finishing  the  work.  The  total  time 
from  the  commencement  of  drilling  until  the  blast  is  cleaned  out 
averages  28 J  hours.  Of  the  110  tons  hoisted  only  10  per  cent, 
is  water.  In  estimating  the  tonnage  260  cu.  ft.  are  reckoned  per 
foot  sunk,  except  where  the  conditions  are  such  as  to  increase 
the  average  cross-sectional  area  of  the  shaft. 

"Following  the  sump  shift,  as  just  described,  the  rock  drill 


EXAMPLES  OF  ROCK   DRILL     PRACTICE  245 

men  proceed  with  the  benches  —  one  bar  being  rigged  on  each 
bench  —  which  are  generally  dislodged  with  eight  holes  each. 
Care  is  taken  to  give  the  end  holes  the  full  length  of  drill,  so  that 
the  ends  of  the  shaft  will  be  left  low  and  the  sump  high.  It 
should  be  mentioned  that  hand  labor  is  also  put  to  work  on  the 
sump,  shaping  the  shaft  and  easing  the  sockets,  which  are 
reblasted  when  benches  are  fired.  The  bench  blast  generally  gives 
110  to  115  buckets,  and  the  footage  made  for  the  two  blasts 
during  the  month  of  thirty-one  days  under  review  averages  7.62 
ft.,  making  a  total  for  the  month  of  99.18  ft. 

CONDITIONS  FAVORING  RAPID  SINKING  WITH  AIR  DRILLS 

I  must  now  pass  on  to  a  discussion  of  what  I  believe  to  be  the 
conditions  most  favorable  for  rapid  sinking  with  machines.  Such 
conditions  are: 

(1)  The  maximum  quantity  of  rock  should  be  broken  at  each 
blast.     In  this  way  time  will  be  saved  because  there  will  be  fewer 
delays  in  loading  and  firing  holes,  setting  up  and  tearing  down 
machines,  taking  out  tools  and  workmen,  cleaning  down  timbers, 
and  examining  the  walls  of  the  shaft  after  blasting. 

(2)  By  rightly  judging  the  charge  of  explosive  necessary,  the 
rock  should  be  broken  to .  the  best  size  for  rapid  loading  into 
buckets  or  skips.     However,  the  size  to  which  the  rock  breaks, 
depends  largely  on  the  character  of  the  rock.     Rock  broken  into 
pieces  weighing  from  20  to  200  Ib.  is  most  rapidly  placed  by  hand 
in  buckets,  while  very  fine  rock  must  be  shoveled,  which  takes 
longer. 

Where  water  is  present  in  moderate  quantities,  by  having  a 
large  quantity  of  broken  rock  on  the  shaft  bottom  several  hours 
of  dry  shoveling  can  be  obtained.  The  amount  of  time  lost  in 
dealing  with  even  a  moderate  amount  of  water  is  very  notice- 
able. When  the  sandstones  and  quartzites  of  the  Witwatersrand, 
as  is  often  the  case,  contain  a  considerable  proportion  of  talcose 
and  micaceous  material,  water  converts  the  mass  into  a  pudding- 
like  aggregate  that  must  be  dealt  with  in  the  right  manner  or 
it  is  very  difficult  to  shovel.  In  my  own  experience  I  found 
that  such  ground  would  settle  and  pack  just  as  badly  after  a 
round  of  hand-drilled  holes  had  been  blasted  as  it  would  after 
a  round  of  machine-drilled  holes  has  been  fired. 

Where  rock  of  this  character  is  met  with,  the  best  way  to 


246  ROCK   DRILLS 

deal  with  it  is  by  lowering  a  hose  at  each  end  of  the  shaft  and 
attaching  to  each  hose  a  short  blow-pipe.  The  blow-pipe  is 
stabbed  about  4  in.  into  the  loose  rock  and  the  whole  mass  worked 
over  thus.  It  is  important  also  to  excavate  a  good  sump,  the 
water  in  which  is  either  pumped  or  bailed  out  frequently,  so  that 
the  level  of  the  water  stays  below  that  of  the  broken  rock,  thus 
keeping  it  partially  drained.  By  these  means  even  the  worst 
setting  rock,  that  is  almost  hopeless  to  attack  with  pick  and  shovel 
while  water-logged,  may  be  shoveled  fairly  rapidly. 

(3)  It  will  then  be  obvious  that  the  most  rapid  cleaning  out 
can  be  done  when  there  is  a  maximum  quantity  of  broken  rock 
on  the  bottom,  which  is  easily  available  for  loosening  with  picks 
and  raising  into  the  bucket  by  hand  or  shovel.  It  is  always  the 
last  10  or  15  tons  of  rock  spread  all  over  the  shaft  bottom,  or 
partially  loosened  by  the  blast,  that  takes  the  major  portion  of 
the  time  to  clean  up  and  which  reduces  the  average  tonnage 
hoisted  per  hour.  It  is  obvious,  therefore,  that  if  a  shaft  can  be 
sunk  by  blasting  a  " round"  every  5  ft.,  it  will  be  sunk  quicker 
than  when  a  round  is  blasted  every  4  ft.,  for  the  more  easily  and 
more  quickly  removed  rock  will,  in  the  first  case,  bear  a  greater 
ratio  to  that  portion  of  the  rock  hard  and  slow  to  remove. 
Besides,  less  time  will  be  lost  in  setting  up  and  blasting. 

CONDITIONS  THAT  INFLUENCE  THE  LENGTH  OF  HOLE  TO  BE  USED 

The  question  as  to  what  is  the  most  economical  length  of 
hole  to  drill  in  sinking  a  five-compartment  shaft  must  be  con- 
sidered in  the  light  of  these  and  other  considerations.  We  must 
remember  first  that,  where  two  buckets  are  available  for  hoist- 
ing, most  of  the  actual  time  of  the  drilling  shift  is  occupied  by 
setting  up,  taking  down,  and  sending  up  machine  steel  and  such 
gear  as  bars,  block,  wedges,  etc.  It  must  also  be  remembered 
that,  other  things  being  equal,  it  is  economical  to  drill  long  holes 
instead  of  short  ones.  Less  time  on  the  average  is  lost  setting  up; 
besides,  the  first  few  feet  of  the  hole  occupy  the  greater  part  of 
the  time  in  drilling,  because  the  hole  has  to  be  carefully  "pitched," 
sometimes  a  long  and  tedious  operation  requiring  patience  and 
skill;  then  the  hole  must  be  started  with  a  slow-drilling  star- 
bit  of  large  gage.  It  takes  only  a  few  minutes  of  drilling  to 
lengthen  a  hole  from  6  ft.  to  8  ft.  It  would  appear,  therefore, 
that  the  most  economical  length  of  hole  must  be  found  by  trial. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE  247 

Theoretically  the  length  would  be  such  that  it  will  break  clear 
to  the  bottom  with  one  loading  and  firing. 

Other  factors  have,  however,  to  be  considered.  The  longer 
the  holes  drilled  in •  the  sump,  and  these  are  drilled  at  an  angle 
of  45°  to  35°  from  the  vertical,  the  greater  the  width  of  shaft 
bottom  that  can  be  abridged,  and  the  less  the  number  of  holes 
required  behind  the  sump  holes  to  give  a  fair  burden  between  the 
cut  holes  and  those  for  blasting  out  the  ends  of  the  shaft.  If 
the  space  under  both  hoisting  compartments  can  be  left  avail- 
able for  the  use  of  both  buckets,  gear  can  be  more  rapidly  sent 
up  and  down. 

The  most  fatal  objection,  however,  to  relying  on  this  method 
for  making  the  best  progress  is  the  fact  that,  where  deep  holes 
are  blasted  in  rock,  broken  by  many  jointings,  the  blasts,  explod- 
ing first,  lift  large  slabs  of  rock  even  from  the  ground  behind 
them,  and  so  are  very  apt  to  cut  off  or  tear  out  fuses  from  other 
holes,  thus  causing  misfires. 

But  in  most  cases  misfires  can  be  traced  either  to  defective 
fuse  or  to  old  fuse  in  which  the  rubber  has  rotted  so  that  it  cracks 
when  thrust  into  the  holes.  Fuse  lighted  out  of  proper  rotation, 
and  water  entering  detonators,  also  cause  misfires. 

At  the  Hercules  mine  the  danger  of  drilling  into  missed  holes 
is  guarded  against  by  making  a  rough  sketch  of  the  shaft  bottom 
before  each  firing  showing  the  position  and  direction  of  holes; 
this  is  handed  to  the  foreman  on  the  following  shift. 

THE  MOST  ECONOMICAL  LENGTH  OF  HOLE  TO  USE 

A  certain  percentage  of  misfires  thus  occurs  frequently. 
This  means  that  in  many  cases  a  second  blast  must  be  made; 
and  in  any  case,  it  is  impossible  to  be  sure  that  some  stumps  of 
holes  will  not  be  left.  Of  course  it  may  happen  several  times 
in  succession  that  all  the  holes  "go"  and  also  break  well,  but  this 
cannot  be  depended  on  in  practical  work.  In  these  large  shafts 
it  has  bever  been  found  practical  to  employ  electric  blasting. 
Reliance  is  placed  on  fuses,  the  very  best  quality,  costing  in  South 
Africa  11  cents  per  coil  of  24  ft.,  being  generally  used  here.  Fuses, 
12  ft.  long,  are  used;  double  fuses  are  placed  in  the  leading  holes, 
and  all  are  well  greased  at  the  detonators.  If  a  second  blast  has 
to  be  made,  there  is,  of  course,  a  loss  of  time  involved  in  finding, 
blowing  out,  and  recharging  the  old  holes.  Hence  in  practice 


248  ROCK   DRILLS 

the  best  length  of  hole  to  be  employed  in  shaft  sinking  will  be 
the  longest  that  can  be  conveniently  drilled. 

In  five-compartment  shafts,  about  34  X  9  ft.  between  rock, 
the  most  convenient  length  of  hole  is  bout  10  ft.  for  the  sump 
holes  and  about  8  ft.  for  other  holes.  In  seven-compartment 
shafts  steel  14  ft.  long  is  used  in  drilling  the  cut  holes;  these 
lengths  of  holes  mean  that  the  bottom  of  the  shaft  is  cleaned  up 
once  for  every  3J  to  4  ft.  sunk.  It  often  happens  in  favorable 
ground  that  no  second  blast  is  required,  but  in  very  tough  ground, 
or  when  many  misfires  have  occurred,  a  third  blast  may  some- 
times be  necessary. 

The  practical  objection  to  using  cut  holes,  as  long  as  12  ft., 
and  followed  by  the  breaking  out  holes,  10  ft.  deep,  is  that  in 
hard  ground  the  starters  would  have  to  be  given  a  greater  gage 
than  3i  in.  and  the  total  weight  of  steel  used  would  have  to  be 
much  increased.  The  gages  used  at  its  gold  mines  by  the  Rand 
Collieries,  Ltd.,  are  3J,  2f,  2|,  2J,  2,  If,  and  1J  in.  Besides,  the 
very  long  steel  used  would  be  awkward  to  handle  and  to  send  up 
and  down,  while  the  first  charge  would  be  too  far  down  to  lift  the 
top  half  of  the  burden  on  the  holes. 

For  comparison  I  give  the  costs  of  breaking  and  shoveling 
rock  in  sinking  the  following  shafts.  The  No.  1  shaft  at  the 
Rand  Collieries  and  the  Kleinfontein  Reef  shaft  were  sunk  with 
machines,  the  others  were  sunk  by  hand.  No.  1  shaft,  Rand 
Collieries,  average  for  four  months,  shaft  about  34  X  9ft. ;  ground, 
quartzites  and  amygdaloidal  diabase.  The  average  footage  sunk 
per  month  was  120;  cost  per  ton  10s.  9d.  In  very  hard  diabase, 
103  ft.  were  sunk;  cost  per  ton  12s.  0.2t/.  In  soft  shales,  112  ft. 
were  sunk;  cost  per  ton  8s.  5.5d;  Kleinfontein  Reef  shaft,  34  X  9 
ft.  in  quartzites,  107  ft.  sunk,  cost  per  ton  11s.  7.286V/.;  Brakpan 
mines  shaft,  43  X  9  ft.,  quartzites,  124  ft.  sunk,  cost  per  ton  8s. 
11. 2d.  City  Reef  shaft,  46  X  9  ft.,  125.6  ft.  sunk,  cost  per  ton 
9s.  2d.;  Hercules  shaft,  47  X  9  ft.,  119  ft.  sunk,  cost  per  ton  8s. 
5d.;  Wolhuter  Reef  shaft  46  X  9  ft.,  95  ft.  sunk,  cost  per  ton 
10s.  6d 

SINKING  OF  INCLINED  SHAFTS 

The  rate  and  cost  of  sinking  inclined  shafts  varies  consider- 
ably according  to  circumstances.  The  variations  in  the  strati- 
fication, jointing  and  texture  of  the  quartzites  and  conglomerates; 


EXAMPLES   OF   ROCK   DRILL   PRACTICE  249 

the  presence  of  dikes  and  faults;  the  angle  the  shaft  makes  with 
the  strata;  the  presence  or  absence  of  water  and  the  amount  of 
timber  required  are  important  considerations.  The  angle  of 
the  shaft  itself  to  the  horizon  is  most  important,  the  flatter  the 
angle  the  more  easily  is  the  broken  rock  removed  from  the  face 
and  drilling  again  started.  The  East  shaft  of  the  New  Klein- 
foiitein  mine,  6  X  21  ft.,  was  sunk  213.5  ft.  in  one  month.  The 
angle  or  dip  of  shaft  was  about  30°.  Timbering  consisted  of 
sills  only.  This  was  sunk  in  foot-wall  slates.  The  incline  on  the 
Nigel  Deep,  7  X  14  ft.,  was  sunk  in  foot- wall  slates  which  are 
fairly  hard  and  tough,  breaking  badly.  The  angle  of  dip  was 
15°.  Two  hundred  and  sixty  feet  were  sunk  in  one  month. 

At  the  bottom  of  a  shaft  3100  ft.  deep  at  the  Brakpan  mines 
in  June,  1903,  223  ft.  were  sunk  in  one  month  in  foot- wall  shales 
with  quartzite  hanging  wall.  The  ground  was  hard  and  tough, 
no  timbering,  except  sills,  being  put  in;  a  brattice,  the  lower 
half  of  galvanized  iron  and  the  top  half  of  loosely  hung  canvas, 
which  was  the  only  construction  that  would  stand  the  concus- 
sion from  the  blasts.  The  size  of  shaft  was  7  X  19  ft.;  dip  13°. 
Thus  the  shaft  more  nearly  approximated  a  large  cross-cut.  Six 
3J-in.  Holman  drills  working  from  10  to  13  hours  would  put  in 
31  holes,  the  number  required  to  break  the  face;  a  center  cut,  as 
in  driving,  was  employed,  as  the  ground  was  too  tight  to  allow 
a  V-cut  being  used.  For  223  ft.,  114  cases,  50  Ib.  each,  of  IJ-in. 
gelatine,  were  employed.  The  longest  chisel  used  was  9J  ft. 
Generally  6  to  7  ft.  were  broken  per  round.  The  consumption 
of  gelatine  was  5.4  Ib.  per  ton  of  rock.  In  August,  1908,  261  ft. 
were  sunk  in  the  same  shaft.  Air  pressure  at  the  surface  was 
80  Ib.  per  square  inch.  About  five  hours  were  required  to  clear 
away  the  rock  from  the  blast  before  drilling  could  be  resumed. 
The  contract  price  to  six  rock  drill  miners  for  breaking  the  ground, 
on  the  same  terms  as  for  driving  quoted  above,  was  £4  10s.  per 
ft.  Six  or  seven  holes  formed  the  cut,  three  holes  being  drilled 
to  meet  with  a  4-in.  short  collar  hole  between  them.  The  other 
holes  were  arranged  in  rows  of  three.  The  miners  made  high 
wages  at  this  price. 

STOPING  ON  THE  WITWATERSRAND 

The  width  of  reefs  worked  varies  from  the  inch-wide  South 
reef  on  the  West  Rand,  to  the  large  quarry  stopes  on  the  Rose 


250 


ROCK  DRILLS 


Deep,  shown  in  Fig.  149.     The  angle  of  dip  is  80°  or  over  on  the 
Randfontein  mines  to  practically  flat  reefs  on  the   East  Rand. 


Perhaps  the  average  dip  would  be  about  30°  and  the  majority 
of  stopes  are  worked  at  from  45°  to  25°.  The  general  system  of 
work  is  underhand  or  breast  stoping.  Where  overhand  stgping  is 
employed  (except  for  some  experimental  work  with  air-fed  hammer 
drills),  it  is  used  mainly  in  breaking  down  waste  wall  rock  for 


EXAMPLES   OF  ROCK   DRILL  PRACTICE 


251 


FIG.  150.  —  The  little  Holman  2-inch  diam.,  5-inch  stroke  working 
underground. 


FIG.  151.  — The  Imperial  drill  boring  with  hollow  steel.     Note  the  arrange- 
ment of  the  feed  screw  to  make  a  light  cradle  and  the  slag  attachment. 


252  ROCK  DRILLS 

filling,  and  then  shooting  down  the  ore  on  to  planks  and  stacks. 
Hand  labor  is  usually  employed  for  this  work.  Under  usual 
conditions,  stopes  under  about  48  in.  in  width  are  worked  by 
hand  drills  or  " single  jacking"  with  natives;  but  when  native 
labor  is  scarce  machines  are  employed  in  smaller  stopes.  It  is 
anticipated  that  a  suitable  machine  will  be  evolved  for  work  in 
narrow,  flat  stopes  which  will  enable  a  large  proportion  of  native 
labor  to  be  dispensed  with. 

The  3|-in.  machine  is  usually  employed  for  stoping  in  the 
larger  stopes.  It  is  mounted  on  an  arm  and  saddle  from  a  more 
or  less  vertical  bar  rigged  between  hanging  and  foot-wall  of  the 
stope;  2f  in.,  2J  in.,  and  2  in.  diameter  piston  drills  have  also 
been  employed  in  increasing  numbers  in  narrow  stopes.  See 
Figs.  150  and  151. 

Air  Pressure.  —  Air  pressures  vary  at  the  various  mines.  In 
the  newer  mines  air  at  80  Ib.  pressure  is  often  available  for  develop- 
ment, but  in  the  older  mines  65  to  75-lb.  pressure  is  maintained 
on  the  surface.  Many  machines  are  called  upon  to  operate  at 
as  low  as  40  to  50  Ib.  Air  pressures  have,  however,  been  improved 
recently.  At  the  pressures  available  small  piston  drills  have 
not  been  able  to  drill  sufficient  holes  to  enable  them  to  compete 
in  cheapness  with  hand  labor,  except  in  a  few  instances. 

Shape  of  Stope.  —  Levels  are  driven  from  150  to  300  ft.  apart 
on  the  dip.  The  shapes  which  stopes  assume  vary  greatly  with 
the  conditions  of  roof,  hanging  and  foot-wall  and  pillars  to  be 
left. 

J.  J.  Wilkes  (Jour.  Chem.  Met.  and  Min.  Soc.,  October,  1905) 
gives  the  following  figures  showing  shape  of  stopes.  Fig.  152 


'  "^7vv£r        — 


FIG.  152.  —  Overhead  stoping  on  15°  to  45°  reef. 

shows  overhand  stoping  with  pillars  left  along  the  drive  in  a  reef 
dipping  15°  to  45°.  Figs.  153  and  154  show  a  similar  face  with 
the  benches  carried  at  an  angle  to  the  drive.  Fig.  155  shows  a 


EXAMPLES  OF   ROCK   DRILL  PRACTICE 


253 


stope  with  a  pillar  being  cut  out  by  means  of  a  drive  underneath 
it.  Fig.  156  shows  a  face  working  in,  to  come  down  and  cut  out 
a  lower  drive  pillar.  Fig.  157  shows  a  pillar  being  cut  out  by 
eating  in  under  it.  Fig.  158  shows  a  stope  face  from  pillars  with 


FIG.  153.  FIG.  154. 

FIGS.  153  and  154.  —  Similar  to  Fig.  152,  except  that  benches  are  carried  at 
angle  to  the  drift. 

benches  for  machine   holes  to  be  drilled,  and  a  box  hole  rise 
put  up  from  the  level  below. 

Mr.  Tom.  Johnson  (Jour.  Chem.  Met.  and  Min.  Soc.,  March, 
1908)  gives  the  following: 

"As  to  the  manner  of  carrying  stopes,  with  a  dip  up  to  about 
40°,  I  like  to  see  the  faces  of  benches  bearing  away  about  30° 

from  the  direction  of  full  dip 

(Fig.  159),  greater  in  flatter 
stopes.  The  benches  should 
be  broken  from  the  bottom  of 
the  stope  upwards,  instead  of 
downwards  as  most  miners 
prefer  to  do;  in  working  up- 
wards the  next  bench  above  is 
lengthened,  which  is  an  advan- 
tage as  it  gives  room  for  the 
explosives  to  kick  beyond  the 
bottom  of  the  holes;  in  steep 
stopes  the  angle  of  the  faces 
from  the  direction  of  full  dip 
would  be  less,  Fig.  160.  Stop- 
ing  would  become  more  underhand  in  mines,  where  it  was  not  ad- 
visable to  have  a  large  amount  of  broken  ore  in  the  stopes,  Fig. 
160;  but  in  a  mine  where  the  broken  ore  could  be  left  so  as  to  work 
on  it,  Fig.  161,  then  it  would  be  cheaper  to  allow  the  stoping  to 


FIG.  155.  —  Stope  with  pillar  being  cut 
on  lower  side  at  drive. 


254  ROCK  DRILLS 

become  more  overhand  as  the  dip  became  greater.  As  more  ma- 
chines could  be  got  to  work  comfortably,  time  would  be  saved  in 
clearing  away  the  gear,  and  there  would  be  no  danger  of  the 
workers  slipping  down  the  stope.  Also  the  lower  part  of  the  stope 


FIG.  156.  —  Face  working  in  to  cut  pillar  from  above. 

being  full  of  broken  ore  and  the  workers  close  up  to  the  face,  there 
would  be  less  chance  of  accidents.  Many  accidents  happen  to 
natives  in  the  bottom  of  steep  stopes,  when  underhand  stoping, 
from  tools  slipping  or  pieces  of  rock  from  the  hanging  or  foot- 


E22&  CS23 

V~L\r& 


FIG.  157.  —  Face  working  in  to  cut  pillar  from  above. 

wall  coming  away.  Care  would  be  needed  to  regulate  the  quantity 
of  rock  taken  out  of  the  stope  so  as  not  to  lower  it  too  much,  and 
to  see  that  the  rock  blasted  was  broken  small  enough  to  pass  the 
boxes  freely  without  choking. 


EXAMPLES   OF  ROCK  DRILL   PRACTICE 


255 


"It  might  be  asked,  in  what  manner  would  it  be  best  to  start 
stoping  overhand,  whether  from  the  back  of  drive  or  leave  a  rib 
in?  This  would  depend  a  great  deal  on  the  circumstances  of  each 
place;  it  would  certainly  be  cheaper  to  start  at  the  corner  of  the 
raise  and  take  the  back  of  the  drive  out  and  stull.  In  this  case 
I  should  take  about  4  ft.  out  along  the  back  of  the  drive  well 
ahead  of  the  stope,  blasting  the  rock  on  to  a  temporary  stage 
just  high  enough  for  the  cars  to  go  under,  putting  in  the  perma- 
nent stulling  behind,  taking  care  before  blasting,  either  on  to 
the  temporary  stage  or  permanent  stulling,  to  get  a  cushion  of 
rock  on  the  stage  Fig.  161." 

Ideal  Arrangement   of  Stope.  —  The  ideal  arrangement  of  a 


FIG.  158.  —  Stope  face  with  benches  for  drills. 

stope  would  be  such  that  the  number  of  machines  breaking  ore 
would  always  have  available  a  bench  or  benches  that  would  allow 
of  the  machine  being  set  up,  and  boring  the  maximum  number  of 
holes  possible  during  the  shift,  each  hole  being  given  the  maxi- 
mum economic  burden  and  also  the  maximum  economic  length. 
This  ideal  condition  is  never  attained,  though  it  might  be  added 
that  the  holes  should  be  so  placed  as  to  blast  out  the  rock  in 
the  direction  in  which  the  ore  is  to  be  loaded  and  to  break  it, 
neither  too  fine  for  subsequent  sorting,  nor  so  large  as  to  require 
reboring,  "popping,"  or  "bull-dozing,"  to  reduce  it  to  a  size 
convenient  for  handling. 

Faults  and  the  necessity  of  cutting  pillars  often  spoil  the  face; 
where  a  machine  is  given  less  than  5  ft.  of  face  to  work  on  it  has 
often  to  be  set  up  to  drill  a  narrow  or  shallow  bench  at  a  loss  of 


256  ROCK  DRILLS 

time.     The  following  gives  the  cost  of  running  four  2-in.  machines, 
per  shift,  in  stoping.     Thirty-six  3-ft.  holes  are  drilled  per  shift. 


FIG.  159.  —  Part  of  stope-face  showing  run  of  benches 
30°  from  the  direction  of  full  dip.  Dip.  15°  to  40°. 
The  machines  are  moved  until  the  four  benches 
are  drilled,  and  then  returned  to  No.  1  bench. 

Cost  of  Four 
"  Little  Won- 
der Drills"  per 
Shift. 

Air    (including    compressor    charges    and    depreciation):    four 

machines  at  3s.  3. Id.  per  shift £0  13  0.40 

White  labor:  One  skilled  white  miner    ' 1  0  0 

Native  labor:  Ten  natives  at  3s.  per  shift 1  10  0 

Thirty-six  hammer  boys  and  one  shift  boy  at  3s.  per  shift - 

Oil:  Four  machines  at  lAld.  each 0  0  5.64 

Hoses:  Four  machines  at  3.51d.  each 0  1  2.04 

Maintenance,  taken  at  £2  11s.  4d.  per  machine  per  month,  and 

depreciation  (cost  of  drill  £28,  and  life  estimate  four  years) .  .    0  4  10.16 

Totals £3  9  6.24 

Miners'  Wages.  —  Miners  are  generally  paid  by  the  fathom, 


EXAMPLES   OF   ROCK   DRILL   PRACTICE 


257 


and  the  area  of  all  pillars  is  measured  up  for  them.     Miners  are 

charged  for  explosives,   stores, 

,          ,.  riM.  •  •  i  Higher  side  r/b 

and   natives.     The  price    paid 

varies  from  £3  10s.  to  £2  10s. 
per  fathom.  In  one  instance 
45s.  per  fathom  was  paid,  gel- 
atine being  charged  at  58s. 
per  50-lb.  case;  natives  at  2s. 
9d. ,  other  stores  at  cost ;  fuse  3d. 
to  4:d.  per  coil;  candles  11s.  per 
box.  Prior  to  the  strike  two 
machines  and  five  natives  would 
be  under  the  charge  of  one 

miner.     Now,  according  to  Mr.  _  

Phillips,  one  man  has  to  super-    FlG    160  _  Part  of  underhand  slope. 


intend  three  machines  or  more, 
and  each  machine  must  drill 
five  holes  per  shift,  if  the  con- 
tractor wishes  to  make  any- 
thing on  his  contract.  The 
general  conditions  remain  the  same,  and  these  conditions  are  not 
such  as  to  enable  a  miner  to  put  in  his  five  holes  regularly,  as  they 
cause  a  large  waste  of  time  nearly  every  day.  Given  a  good 


The  top  gets  too  far  back  to  carry 
light  machines  as  the  broken  rock 
would  fall  on  the  lower  benches  and 
need  shoveling  off  before  drilling 
could  commence. 


FIG.  161.  —  Part  of  overhand  stope.  f  Benches  car- 
ried at  such  an  angle  that  all  holes  are  wet,  top 
or  back  of  drive  taken  out  and  strelling  put  in. 

machine,  and  good  air  pressure,  I  find  1.75  in.  per  minute  the 
average  rate  of  drilling,  although  I  have  timed  machines  drilling 
at  rates  varying  from  0.47  up  to  2.4  in.  per  minute.  Taking 


258  ROCK  DRILLS 

the  average,  the  actual  drilling  time  for  a  6-ft.  hole  is  40 
minutes;  therefore,  with  eight  hours  at  his  disposal,  assuming 
9J  hours  for  a  full  shift  and  allowing  1J  hour  for  getting  to 
his  working  face,  charging  up,  etc.,  a  contractor  could  put  in 
12  holes  if  there  were  no  stoppages  of  any  kind.  Now,  of 
course,  it  is  obvious  that  a  machine  cannot  be  drilling  con- 
stantly, but  it  is  also  obvious  that  there  must  be  a  considerable 
waste  of  time  if  it  takes  eight  hours  to  do  two  hours  and  forty 
minutes'  drilling.  A  fair  time  allowance  for  work,  incidental  to 
running  a  machine,  is,  I  think,  the  following:  three-quarters  of 
an  hour  for  rigging  up  and  oiling  the  machine,  five  minutes  for 
changing  drills,  and  ten  minutes  for  shifting  the  machine  on  the 
bar  to  start  a  new  hole;  this  would  give  an  average  of  a  little 
over  an  hour  per  hole,  excluding  rigging  up,  or  time  for  six  holes 
per  shift  and  two  rigs. 

ROCK-DKILL  PRACTICE  IN  AUSTRALIA 

The  Ingersoll-Sergeant,  Holman,  Sullivan,  and  Taylor-Hors- 
field  rock  drills  are  generally  employed.  In  Victoria  generally 
one  star  bit  followed  by  chisels  only  are  used.  Leyner  hammer 
drills  were  for  a  time  in  use  on  the  Star  of  East  mine  and  the  Long 
Tunnel  mine.  W.  A.  T.  Davis  gives  the  following  notes  on 
the  arrangement  of  holes  and  blasting  method  in  use  in  West 
Australia: 

"In  driving,  the  'triangle'  cut  is  usually  preferable  to  the 
'V  cut,  Fig  162,  as  there  are  less  dry  holes  to  bore,  than  to  the 
'drag'  cut,  Figs  167-168,  because  a  greater  quantity  of  ground 
can  be  broken  in  a  given  time  with  less  boring;  nevertheless  the 
drag  cut  is  often  used  to  advantage,  especially  where  there  is  a 
wall  or  dig  in  the  face  to  bore  to.  For  sinking,  in  faces  of 
large  area,  the  V  or  center  cut,  Fig.  162,  is  usually  preferable, 
more  especially  where  there  are  electrical  appliances  for  firing, 
and  where  there  are  no  walls  or  natural  fractures  in  the  rock 
to  bore  to.  Further,  the  'cut  opening'  is  the  full  width  of 
the  face,  which  is  not  the  case  with  other  cuts.  The  V  is 
also  preferable  to  the  drag  cut,  because  more  ground  is 
broken  by  one  rigging  of  the  bar  or  column.  It  is,  never- 
theless, very  destructive  to  timber  in  the  locality.  In  sinking 
where  no  electric  battery  is  in  use  and  there  is  a  quantity 
of  water  to  contend  with,  the  drag  cut  is  often  adopted  and  used 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


259 


to  advantage,  as  the  water  is  always  confined  to  one  end  of  the 
shaft.  In  rising,  the  triangle  cut  is  usually  adopted  in  preference 
to  the  drag  cut,  as  there  is  not  the  difficulty  in  collaring  the  holes, 
the  face  being  always  at  right  angles  to  the  machine  drill.  In 
stoping,  the  general  stope  or  drag  cut  is  used;  the  holes  should 
be  horizontally  zigzag,  vertically  in  line.  In  stoping  hard^ground 
a  considerable  saving  can  often  be  effected  where  holes  are  all 
'water  holes/  by  having  the  stope  face  a  good  hight  and  fol- 
lowing up  the  same  line  of  holes  after  each  firing  until  the  stope 
has  'run  out.' 


FIG.  162.  —  Shaft  sinking  method,  V  cut. 

"In  the  general  use  of  the  triangle  and  V  cuts,  the  center 
holes  should  always  be  fired  first  and  cleaned  up,  thus  giving  the 
surrounding  holes  clearance  and  more  freedom.  In  some  cases  a 
marked  saving  can  be  effected  by  boring  the  center  holes,  remov- 
ing the  machines,  firing  and  cleaning  up  same;  better  judgment 
can  then  be  formed  in  boring  out  the  remainder  of  the  cut,  a  con- 
siderable amount  of  boring  and  explosives  thus  being  saved. 
The  loss  of  20  or  30  minutes  through  the  second  rigging  of  the 
machine  is  more  than  compensated  for  by  the  above  advantages." 

Firing.  —  This  should  in  most  cases  be  carried  out  in  two  sec- 
tions. The  system,  though  occupying  a  little  more  time,  is  wise, 
as  a  whole  round  may  be  destroyed  by  a  misfire,  throwing  double 


260  ROCK   DRILLS 

burden  upon  the  nearest  holes,  and  thus  ineffectively  breaking 
the  ground  and  spoiling  the  shape  of  the  face  for  the  next  boring 
out,  thus  resulting  in  loss  of  time  and  costly  work. 

ROCK-DRILL  PRACTICE  IN  BROKEN  HILL,  NEW   SOUTH  WALES 

When  I  was  on  that  field  some  years  ago  the  practice  was 
poor.  Air  pressures  were  low  and  pipes  much  too  small,  with 
numerous  angles  and  bends  in  them.  Holes  were  put  in  too 
short.  I  do  not  know  where  more  recent  figures  have  been  made 

public. 

PRACTICE  ON  THE  KALGOOHLIE  FIELD 

E.  Davenport  Cleland  writes  in  the  monthly  journal  of  the 
West  Australian  Chamber  of  Mines  as  follows: 

"By  using  the  'stope-cut/  Fig.  163,  it  is  a  simple  matter  to 
maintain  one  end  of  the  shaft  deeper  than  the  other,  and  thus 
facilitate  the  bailing  of  water  and  the  filling  of  buckets  with 
broken  rock.  And  when  firing  out  the  bottom,  the  rock  is  pro- 
jected against  the  end  of  the  shaft  and  not  so  directly  upwards 
as  would  be  the  case  with  center  cuts,  and  therefore  there  is  not 
so  much  risk  of  damaging  the  timber  overhead. 

"The  boring  of  the  shaft  is  universally  performed  by  means  of 
machine-drills.  These  are  3f  in.  diameter,  and  are  operated 
by  compressed  air  at  a  pressure  ranging  from  80  Ib.  to  90  Ib.  per 
square  inch.  The  diameter  of  steel  used  varies,  according  to 
the  kind  of  rock  to  be  bored,  from  Ij  in.  to  2j  in. 

"Both  cruciform  and  chisel-shaped  bits  are  used,  though  on 
some  mines  the  cruciform  bit  is  not  in  favor.  The  first,  or  t  pitch- 
ing' bits,  bore  to  a  diameter  of  If  in.,  second  bits  to  li  in.,  third 
bits  to  Is  in.,  and  the  finishing  bit  to  lj  in. 

"Slope-cut.  —  In  this  method,  as  shown  in  Fig.  163,  the 
stretcher-bar  and  machine  are  fixed  at  a  distance  of  about  2  ft. 
from  one  end  of  the  shaft.  From  this  point  the  total  number  of 
holes  required  for  the  first  cut  are  drilled.  As  a  rule,  11  are 
necessary.  The  two  holes  marked  A  are  bored  so  as  to  incline 
at  a  rather  flat  angle  towards  the  center  of  the  shaft.  Rows  B 
and  C  are  bored  to  greater  depths,  and  at  steeper  angles,  respect- 
ively; and  the  row  D,  quite  at  the  end  of  the  shaft,  is  vertical, 
or  with  a  slight  inclination  outwards,  so  as  to  keep  the  end  of  the 
shaft  well  open.  The  depth  of  this  row  of  holes  would  be  about 
6  ft.  The  shaft  is  14  by  5  ft.  9  in. 


EXAMPLES   OF  ROCK   DRILL   PRACTICE 


261 


"The  two  holes  A  —  constituting  the  cut  —  are  fired  and  the 
rock  cleaned  out.     The  firing  of  rows  B,  C,  D,  follows  in  rotation, 


a  ••  Effect  of  firing  hoies 
A.B.G.Q 


Showing  position  cf  cfri// ho/es 
FIG.  163.  —  Stope  cut  as  used  on  Kalgoorlie  field. 

and  they  are  cleaned  up  as  fired.     The  excavation  resulting  from 
this  operation  is  shown  in  Fig.  163. 


262  ROCK  DRILLS 

"In  taking  out  the  second  cut,  the  machine  is  rigged  at  the 
opposite  end  of  the  shaft,  and  boring  proceeds  as  in  the  first  cut, 
but  with  the  difference  that  now  only  three  rows  of  holes,  marked 
E,  F,  G,  are  required,  and  a  total  number  of  9  as  against  11 
in  the  first  cut.  Rows  E  and  F  also  are  deeper  and  laid  at  a 
natter  angle  than  those  in  the  first  cut.  This  is  rendered  possible 
because  they  are  firing  to  a  face,  and  the  tearing  of  the  rock  is 
greatly  facilitated  by  the  removal  of  the  first  cut. 

"The  total  number  of  holes  required  is  20.  The  average  depth 
to  which  the  shaft  is  deepened  on  the  completion  of  the  second 
cut  is  5  ft.  in  country  that  is  recognized  as  being  very  hard." 

GOLDEN  HORSESHOE  MINE,  WEST  AUSTRALIA 

It  will  be  noted  in  the  accompanying  table  that  the  size  of 
drill  used  is  3f-in.  diameter  piston,  owing  to  the  hard  ground 
met  with.  It  will  be  seen  that  even  four  drills  were  sharpened 
per  hole,  showing  that  the  drillers  had  a  fair  supply  of  sharp 
steel.  Yet  the  footage  bored  per  eight-hour  shift  is  lower  than 
on  the  Rand.  This  is  largely  due,  first,  to  shorter  working  hours; 
second,  to  some  of  the  work  being  done  in  nearly  vertical  stopes 
which  rendered  erecting  and  moving  drills  more  difficult.  The 
average  ground  is  as  hard  or  harder  than  that  on  the  Rand. 

Drilling  and  Blasting.  —  The  following  figures,  kindly  supplied 
by  Mr.  Sutherland,  manager  of  the  Golden  Horseshoe,  are  instruct- 
ive. The  average  width  of  the  lode  in  this  mine  is  about  12  ft. 

WORK  OF  NEW  INGERSOLL,  3|,  F.  9,  ROCK  DRILLS  IN  STOPES  FROM 
JANUARY  1  TO  JULY  31,  1906.      (GOLDEN   HORSESHOE   MINE) 

Average  number  of  machines  in  use 19.2 

Number  of  shifts 541 

Number  of  holes  drilled    31,660 

Number  of  feet  drilled 217,280 

Feet  drilled  per  drill  per  shift    20.94 

Average  depth  of  holes 6.86 

Tons  of  ore  broken  . 149,313 

Average  tonnage  per  drill  per  shift 14.39 

Steel  sharpened: 

Hand  drills    79,151 

Machine  drills 130,094 

Picks  pointed 694 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


263 


EXPLOSIVES  USED  IN  THE  GOLDEN  HORSESHOE  FROM  JANUARY  1  TO 
JULY  31,  1906 


Sloping 

Driving 

Cross- 
cutting 

Winzing 
and 
Raising 

Shaft 
Sinking 

Plat 
Cutting 

Tons  of  ore  broken 

149,313 

-~—_  .  

Footage    
Pounds  of  explosives  used: 
Gelignite  
Gelatine  dynamite 

89,580 
130 

2,175 

1,210 

5,885 

434 

140 
450 

1,578| 

995 
260 

103i 
50 

3,350  cu.  ft. 

Blasting  gelatine  
Detonators                        .    . 

890 
52,525 

21,975 
10,100 

5,125 
2,200 

9,195 
6,875 

1,750 
700 

200 

Coils  of  fuse 

11,575 

2,320 

552 

1,401 

203 

33 

Average   pounds   of   explo- 
sives per  ton  of  ore  broken 
Pounds    of    explosives    per 
foot  progressed   

.61 

13.37 

13.17 

6.62 

17.39 

4.375 

RECORD  SHAFT  SINKING  AT  THE  VICTORIA  REEF  QUARTZ  MINING 
COMPANY/  AUSTRALIA 

The  work  of  shaft  sinking  was  commenced  (from  the  4024 
plat)  at  4048  ft.  from  the  surface  and  was  continued  until  the 
depth  of  4300  ft.  was  reached  in  one  lift  of  252  ft.  Two  plats 
also  were  cut.  Size  of  shaft  within  the  timbers  10  ft.  7  in.  X  4  ft., 
and  divided  into  three  compartments.  From  the  time  of  start- 
ing (working  only  two  shifts  per  day)  twenty  weeks  were  occupied, 
and  at  the  end  of  that  time  the  cages  were  running  to  the  bottom. 
Putting  in  pent  house,  etc.,  was  included  in  this  time. 


Two 

Plats 

Shaft, 

Totals 

Cost 

Per 

Foot 

Wages 

£  87 
35 

10 
29 

9 
0 

6 
12 

9 

4 

1 
3 

£  787 
315 
167 
92 
99 

*2 

3 

12 
1 

10 

0 
2 
5 
5 
2 

£3 

1 

0 
0 
0 

2 

5 
13 
7 

7 

6 
0 
3 
4 
11 

£  874   17  9 
749     5  9 

Firewood    
Shaft  timber   . 

Explosives  . 

Sundries 

Totals  .          

162 

8 

5 

£1461 

9 

2 

£5 

10 

0 

£1624     3  6 

Taylor  Horsfield's  Catalogue. 


264  ROCK  DRILLS 

SINKING  AN  INCLINE  SHAFT  AT  THE  LONG  TUNNEL  MINE, 
WALHALLA1,  AUSTRALIA 

The  country  rock  consists  of  hard  slates  and  sandstones 
(Silurian),  with  bars  of  "el van,"  and  is  regarded  as  bad  drilling 
rock.  The  total  depth,  sunk  at  an  angle  of  49°  from  the  hori- 
zontal, is  2886  ft.,  and  the  time  occupied  in  this  work,  twenty 
months.  The  first  2300  ft.  of  the  shaft  was  sunk  in  two  sections 
at  once,  and  the  last  586  ft.  sunk  in  one  section.  The  work  was 
carried  forward  by  contractors  working  three  shifts  of  eight  hours 
each  for  six  days  per  week.  Six  Victorian  miners  were  employed 
in  each  shift  to  do  all  of  the  work  of  sinking,  cleaning  up,  and 
fitting  timbers  as  the  shaft  proceeded. 

Two  3J  rock  drills  were  used  at  one  time  in  each  section  for 
the  first  2000  ft.,  and  three  machines  of  the  same  sizes  for  the 
remaining  distance.  The  machines  were  made  by  Taylor  Hors- 
field,  Bendigo.  The  pressure  of  air  at  the  drills  was  100  Ib.  per 
square  inch.  Size  of  shaft  inside  of  timbers  14  ft.  by  5  ft.;  size 
of  timbers  8  in.  by  8  in.  in  frame;  sets  4  ft.  6  in.  apart.  The 
shaft  is  divided  into  three  compartments,  the  total  width  of  rock 
excavated  being  16  ft.  by  7  ft.  The  total  cost  of  repairs  to  rock 
drills  was  £144,  or  about  Is.  per  foot. 

The  explosives  used  were  500  50-lb.  cases  of  Nobel's  Glasgow 
dynamite,  costing  £1500.  Detonators  to  the  number  of  17,200 
were  used,  costing  £30  Is.  3d.  Fuse  cost  per  foot  of  shaft  10.75rf., 
and  candles  (Rangoon)  cost  the  same  amount  for  each  foot  of  sink- 
ing, viz.,  10.75d. 

Size  of  Octagon  steel  used,  lj  in.  and  1J  in.,  with  chisel  bits. 
Total  cost  of  steel  £50.  Average  depth  of  holes  bored,  5  ft.  6  in., 
and  diameters  If  in.  Number  of  holes  fired  (per  shift)  30  in 
three  rounds  of  10  each.  Average  rate  of  pay  per  shift  for  all 
wages  men,  11s. 

SCOTLAND 

GRANITE  QUARRYING  IN  ABERDEENSHIRE,  SCOTLAND  2 

The  methods  here  employed  are  similar  to  the  ones  used  in 
the  United  States.  This  example  is  introduced  to  show  varia- 
tions in  methods  of  breaking  rock  to  suit  different  ends. 

1  J.  Findlayson,  Taylor  Horsfield's  Catalogue. 

2  BY  WILLIAM  SIMPSON,  Eng.  and  Min.  Journ.  Aug.  31,  1907. 


EXAMPLES  OF  ROCK   DRILL   PRACTICE 


265 


Excavation.  —  The  rock  is  removed  by  boring  and  blasting, 
and  for  this  purpose  the  working  face  is  usually  divided  into  two 
benches.  The  top  bench  is  first  worked  back  to  meet  a  good 

\  Main  Floor  Level 


Elevation 


Section 


Feet  10      0 


40  60  Feet 


FIG.  163a.  —  Rubislaw  quarry,  showing  working  face. 

vertical  joint,  a  distance  generally  of  20  to  30  ft.  from  the  face, 
after  which  the  bottom  bench  is  excavated  and  the  rock  entirely 
removed  down  to  the  level  of  the  floor  of  the  dip,  Fig.  163a.  Ver- 
tical shot  holes  up  to  21  ft.  deep  are  used  to  blast  out  the  upper 
parts  of  the  benches,  and  breast  holes  to  remove  the  basal  parts 


Quarry 


Elevation 


mpZLJ^fo 


Section 


FIG.  1636.  —  Method  of  drilling  breast  shot-holes. 

of  the  working  face  where  there  are  no  bed  joints.  These  latter 
are  placed  at  an  inclination  of  about  10°  to  15°  to  the  horizontal, 
and  are  drilled  up  to  21  ft.  long,  as  the  nature  of  the  rock  may 
require,  Fig.  1636,  and  are  calculated  to  increase  the  efficiency 


266 


ROCK  DRILLS 


of  the  blast  and  level  up  the  quarry  floor.  As  it  is  not  convenient 
to  use  the  ordinary  rock-drill  tripod  for  such  holes,  a  special  frame, 
Fig.  163c,  made  of  timber  is  employed,  on  which  the  rock  drill  is 
mounted,  the  frame  being  loaded  with  stones  to  steady  it,  Fig. 
1636.  As  the  rock  is  blasted  out  the  blocks  are  lifted  from  the 
working  face  by  cranes  and  cableways,  but  the  larger  masses, 
beyond  the  power  of  the  lifting  appliances,  are  broken  up. 

Rock  Drilling.  —  The  drilling  of  shot  holes  is  done  by  power 
drills  worked  either  by  steam  or  compressed  air.  Hand  drilling 
is  only  resorted  to  where  it  is  impossible  or  inconvenient  to  use 


Elevation 


Plan 


FIG.  163c.  —  Drill  frame  for  boring  breast  shot-holes. 

a  machine  drill,  as  in  bringing  down  dangerous  parts  of  the 
quarry  wall.  The  machine  drills  are  chiefly  of  the  Ingersoll  or 
Henderson  types,  and  the  usual  motive  power  is  steam. 

The  drill  bits  used  are  the  chisel,  cross,  and  Y  forms.  The 
practice  of  the  various  quarries  in  the  application  of  these  bits 
to  drill  a  hole  differs  considerably,  some  preferring  to  use  almost 
exclusively  the  cross-bit  throughout,  but,  more  commonly,  holes 
are  started  with  cross  or  Y  bits  and  finished,  if  deep,  with  chisel 
bits  for  about  the  latter  half  of  the  hole.  The  results,  however, 
in  the  speed  of  drilling  do  not  vary  much,  as  a  hole  21  ft.  deep 
takes  on  an  average  about  a  working  day  of  ten  hours  to  com- 
plete under  ordinary  circumstances,  the  speed  of  drilling  being 
higher  than  this  average  at  the  beginning,  and  less  at  the  end. 


EXAMPLES  OF  ROCK  DRILL    PRACTICE  267 

In  drilling  a  shot  hole  a  change  of  bit  is  made  at  every  foot 
of  depth  drilled,  and  the  successive  diameters  are  gradually  de- 
creased by  yV  in.,  owing  to  the  conicity  of  the  hole  caused  by  the 
wear  of  the  bit,  so  that  a  hole  21  ft.  deep  started  with  a  3j-in. 
diameter  bit  terminates  with  one  2-in.  diameter.  Water  is 
removed  from  the  shot  holes  by  a  small  iron-closed  bucket,  from 
9  to  18  in.  long,  made  from  a  piece  of  tube  1?  in.  diameter,  let 
down  by  a  light  chain,  and  the  sludge  by  a  sludge  pump  and 
sludge  spoons  of  various  lengths.  The  sludge  pump  consists  of 
a  piece  of  iron  tube  from  4  to  6  ft.  long,  and  If -in.  diameter, 
fitted  with  a  plunger  and  long  iron  handle.  The  end  is  conical, 
with  an  inlet  hole  of  |  in.  diameter. 

Blasting.  —  In  quarrying  granite  the  main  object  is  to  obtain 
large  blocks,  and  explosives  must  therefore  be  applied  judiciously 
and  in  a  sparing  manner.  Coarse  gunpowder  is  used  in  the  Aber- 
deenshire  quarries  for  blasting  purposes  as  higher  grade  explosives, 
such  as  dynamite  and  gelignite,  shatter  the  rock  too  much,  and 
are  not  used  at  all,  except  to  blast  away  bad  rock  or  in  very  wet 
places.  No  general  formula  can  be  given  to  determine  precisely 
the  amount  of  the  charge  for  a  blast,  owing  to  the  very  irregular 
nature  of  the  rock,  but  it  is  estimated  that  one  pound  of  gun- 
powder should  produce  eight  tons  of  rock  under  ordinary  condi- 
tions of  quarrying.  In  blasting  out  a  long  face,  vertical  holes  are 
drilled  down  to  the  horizontal  bed  joint,  and  at  a  distance  back 
from  the  working  face  generally  equal  to  their  depth,  and  small 
charges  of  gunpowder  used,  the  object  being  to  heave  the  mass  on 
its  bed  without  shattering  it.  If  one  end  of  a  working  face  is 
bound,  as  is  sometimes  the  case,  a  narrow  trench  is  blasted  forcibly 
out  between  the  quarry  wall  and  the  working  face  to  permit  this 
method  of  blasting  being  carried  out.  The  mass  having  thus 
been  shaken  and  the  joints  developed,  it  can  be  blasted  off  into 
smaller  blocks,  and  dragged  from  the  face.  For  breast  blasting, 
where  there  are  no  natural  bed  joints,  the  shot  holes  are  usually 
placed  in  line  close  together  with  about  1J  in.  of  clearance  be- 
tween each  at  the  top,  but  both  the  position  and  number  are 
decided  by  the  actual  rock  joints,  and  the  quantity  of  material 
to  be  dislodged.  Groups  of  three,  five,  and  seven  holes  are  com- 
mon, and  these  may  be  drilled  parallel,  radially,  or  in  different 
planes.  If  dry,  vertical  shot  holes  are  filled  directly  from  the  top 
with  loose  powder  passed  through  a  copper  filler,  but  in  the  case 


268  ROCK    DRILLS 

of  wet  holes,  both  vertical  and  inclined,  the  powder  is  made  up 
into  a  cartridge  by  filling  it  into  thin  waterproof  tubing,  and 
tying  the  ends  securely.  Dry  breast  holes  are  loaded  from  a  piece 
of  open  -end  copper  tube,  1J  in.  in  diameter,  fixed  on  the  end  of 
a  long  wooden  rod.  The  regular  shot  holes  are  fired  electrically, 
and  the  detonator  or  electric  fuse  is  placed  about  9  in.  from  the 
surface  of  the  charge  in  the  loose  holes,  and  is  tied  up  with  the 
cartridge  in  wet  holes.  At  some  quarries  a  time  fuse  is  also 
inserted  into  the  charge  of  each  shot  hole  as  a  safeguard  against 
electrical  misfire.  The  charge  is  rammed  home  with  a  timber 
ramrod,  and  the  holes  are  stemmed  or  tamped  with  granite  dust. 
The  electric  wires  of  the  shot  holes  are  connected  up  in  series, 
this  method  being  preferred  to  the  parallel  system,  and  the  charges 
are  fired  by  a  high-tension  electric  exploder.  The  firing  is  done 
either  during  meal  hours,  or  when  work  has  been  stopped  for  the 
day,  unless  the  nature  of  the  blast  is  such  that  the  men  can  readily 
find  safe  cover  in  the  quarry.  A  steam-jet  is  used  at  some  of 
the  quarries  for  effectively  washing  out  the  tamping  and  charge 
of  a  misfire  shot  hole,  instead  of  boring  a  new  one  alongside. 


XIII 

EXAMPLES  OF  ROCK  DRILL  PRACTICE  —  AMERICA 
CALEDONIA  MINE,  NEW  YORK 

Character  of  Rock.  —  The  mining  of  hematite  ore  is  carried 
on  quite  extensively  in  New  York.  The  ore  is  massive,  hard, 
blue  specular  variety,  interspersed  with  stringers  of  calcite,  and 
is  usually  pockety.  A  portion  of  the  ore  is  micaceous  and  almost 
as  soft  as  clay.  The  hanging  wall  is  Potsdam  sandstone,  and 
the  foot-wall  is  crystalline  limestone,  with  some  serpentine. 

Robert  B.  Brinsmade  gives  the  following  account  of  the  drill 
practice  at  this  mine:1 

Drifting  and  Sloping.  —  The  method  of  ore  extraction  now 
used  in  the  Caledonia  mine,  which  was  the  first  to  apply  it,  is 
as  follows:  Every  40  or  50  ft.  along  the  incline  (when  in  ore)  a 
drift  wide  enough  to  reach  from  the  limestone  foot  to  the  serpen- 
tine hanging  wall  is  started,  and  of  sufficient  hight  to  allow  an 
arched  roof,  Fig.  164.  When  a  drift  has  advanced  far  enough 
from  the  incline  to  leave  a  sufficient  pillar,  as  at  D,  a  raise  is  started 
and  driven  just  under  the  hanging  wall  to  the  level  above  at  C. 
When  this  raise  has  been  holed  through,  one  drill  is  started  at 
the  top  and  (with  down-holes  and  underhand  stoping)  the  ore 
is  broken  off  clean  down  to  the  foot -wall,  except  a  narrow  bench 
left  at  the  top,  as  at  R.  Simultaneously,  another  drift  is  cutting 
underhand  benches  at  G  to  extend  the  stope  to  its  full  length. 
When  a  stope  is  cut  as  long  in  the  strike  as  the  roof  will  stand, 
it  is  squared  down,  as  at  J-K,  preparatory  to  starting  another 
drift  and  raise  under  a  new  pillar,  as  at  L-M. 

This  system  conforms  well  to  the  pockety  nature  of  the  deposit. 
When  the  ore  has  pinched  out,  as  at  A7",  the  drift  is  not  continued 
beyond  the  end  of  the  stope,  but  the  advancing  for  the  levels 
below  is  done  at  P,  where  there  is  still  ore  in  the  face.  Each 
stope  has,  as  far  as  possible,  a  pillar  below  it,  as  shown  in 
Fig.  164. 

1  Eng.  and  Min.  Journ.,  Sept.  15  and  22,  1906. 
269 


270 


ROCK  DRILLS 


Drilling.  —  In  shaft  sinking,  the  limestone  foot-wall  is  followed, 
and  a  cross-section  of  18  X  8  ft.  is  excavated.  The  center  cut  sys- 
tem is  pursued  and  two  drills,  with  two  men  on  each,  are  set  on 
vertical  columns  to  drill  during  the  day  shift  the  four  to  six  8-ft. 
holes  necessary  for  each  side  of  the  cut.  The  cut  is  blasted  by 
electricity  at  5.20  P.M.  and  the  debris  cleaned  up  by  muckers 
on  the  night  shift.  On  the  next  day  shift,  the  five  to  six  end 
holes  to  complete  the  round  are  drilled  by  each  machine,  blasted 
and  mucked  out  the  following  night.  This  speed  is  for  soft  hema- 
tite; when  the  face  is  specular  ore  it  may  take  five  or  six  shifts 
to  finish  a  round  instead  of  four.  These  hindrances  render  it 
difficult  to  average  an  advance  exceeding  12  ft.  per  week  of  13 
shifts,  or  117J  hours  actual  working  time. 


Section  on  ABCDEF  Longitudinal  Section 

FIG.  164.  —  Ore  extraction  system  Caledonia  mine. 

In  drifting,  the  common  method  of  four  horizontal  rows  of 
three  6  to  8-ft.  holes  is  used;  one  drill  on  a  vertical  column,  set 
but  once  for  a  round,  does  the  drilling.  The  second  row  from  the 
bottom  is  pointed  down  about  45°  for  the  cut  and  is  fired  first, 
followed  by  the  bottom,  third,  and  top  rows  in  order.  For  soft 
ground  nine  holes  are  enough,  the  center  hole  of  the  second,  third, 
and  top  rows  being  omitted.  When  the  drift  exceeds  8  ft.  in 
hight,  a  heading  is  advanced  above  and  the  floor  is  cut  up  behind 
by  lifters;  or,  in  case  of  a  thick  floor  bench,  by  vertical  down- 
holes. 

The  raises  are  at  least  6  ft.  high  and  10  ft.  wide  to  admit  of 
easy  breaking  for  one  drill.  No  regular  system  of  placing  holes 
is  in  vogue;  the  bottom,  side,  or  top  cut  being  taken  to  best  break 
the  ground,  with  the  drill  column  set  vertically  and  usually  but 
once  a  round. 


EXAMPLES   OF  ROCK   DRILL    PRACTICE  271 

In  the  underhand  sloping  the  holes  are  seldom  quite  vertical, 
or  over  8  ft.  long,  as  the  irregularity  and  low  dip  in  many  places 
of  the  foot-wall  make  the  regular  vertical  benches  and  deep  holes 
of  an  open  quarry  impracticable. 

In  this  mine  there  are  eight  McKieran  rock  drills  of  3-in. 
size;  it  being  found  that  the  2J-in.  size,  though  lighter  to  carry 
around  the  stopes,  could  not  economically  be  made  to  strike 
a  heavy  enough  blow  in  the  hard  specular  ore.  The  rate  of  drill- 
ing varies  with  the  ground.  In  the  red  ore,  seven  6-ft.  holes  per 
shift  are  as  easily  put  down  as  are  two  6-ft.  holes  in  the  hardest 
specular;  uppers,  sufficiently  steep  to  shed  the  dust,  and  down 
waterholes,  drill  faster  than  flat  holes,  as  is  usually  the  case. 
Before  loading,  the  holes  are  freed  from  cuttings  by  a  wooden 
swab;  down-holes  are  blown  out  by  a  1-in.  pipe,  attached  to  the 
compressed  air  hose. 

In  sinking,  drifting,  and  raising,  the  double  screw  with  arm 
is  in  use,  all  new  orders  are  made  of  4-in.  wrought-iron  pipes, 
but  to  utilize  the  old  3-in.  column  arms  and  fittings  (formerly 
employed  on  the  discarded  2J-in.  drills)  extra  heavy  3-in.  pipe 
was  ordered,  and  found  to  be  steady  enough  for  the  large  drill, 
even  when  in  8-ft.  lengths.  For  drilling  on  the  underhand  benches, 
tripods  are  usually  necessary;  but  the  drillers  prefer  to  stand  on 
them  to  make  them  steady  in  operation,  rather  than  to  put  on 
their  legs  the  customary  counterweights.  The  constant  breaking 
of  the  set-screws  in  the  extension  legs  of  the  tripods  was  almost 
entirely  prevented  by  the  substitution  of  soft-iron  round  bars  for 
the  old  drill  butts  the  drillers  insisted  on  using  for  extension. 

Blasting.  —  Electric  caps  are  used  only  in  shaft  sinking;  else- 
where the  heavy  shocks  of  simultaneous  firing  shake  up  the 
serpentine  roof  too  much  to  be  safe.  " Silver  medal"  caps  and 
single-tape  fuse  are  in  vogue,  the  fuse  being  cut  in  equal  4  to  6-ft. 
lengths  and  its  split  ends  ignited  in  the  order  required  by  the 
round  of  holes.  Double-tape  fuse  is  kept  for  wet  down-holes,  as 
it  saves  the  careful  drying  before  loading  essential  for  the  single- 
tape  variety. 

The  drillers  are  erstwhile  Austrian  farmers,  whose  mining 
knowledge  is  limited  to  putting  in  and  loading  the  machine  holes; 
hence  the  placing  of  the  holes  and  the  quantity  of  powder  to  use 
must  be  directed  by  the  American  shift  boss.  Everything  is 
blasted  with  40  per  cent,  dynamite,  except  the  shaft,  drift,  and 


272 


ROCK   DRILLS 


raise  cuts  in  specular  ore,  which  are  broken  by  50  per  cent.,  with 
60  per  cent,  for  the  primer  cartridges.  Three  half-pound  sticks  will 
usually  break  a  6-ft.  hole,  when  firmly  tamped  with  a  small  clay  ball. 

Blasting  (except  for  block  holes)  is  done  generally  just  before 
the  end  of  the  shift,  each  pair  of  drillers  touching  off  their  own 
holes  on  a  signal  from  the  shift  boss.  Misfires,  arising  from  the 
failure  of  the  cap  to  explode,  are  blasted  at  the  beginning  of  the 
next  shift  by  inserting  a  new  fuse  and  primer  cartridge  after 
removing  the  clay  tamping. 

Compressed  Air.  —  The  air  is  kept  at  60  lb.,  which  will  do  the 
work  and  is  more  economical  for  single-stage  compression  than 
a  higher  pressure.  Cooling  water  for  the  air  cylinder  jackets  of 
both  compressors  is  circulated  from  a  cistern  under  the  engine 
room  by  a  4|-in.  Blake  pump. 

The  air  goes  down  the  incline  through  a  3j-in.  wrought-iron 
pipe,  from  which  the  2J-in.  main  leading  into  each  working  level 
can  be  shut  off  by  a  2|-in.  iron  body  gate  valve.  On  the  end  of 
the  level  main,  at  a  safe  distance  from  the  working  face,  is  screwed 
a  2J-in.  branch  tee,  with  three  IJ-in.  and  one  2|-in.  openings, 
from  which  a  1-in.  pipe  goes  off  to  each  drill,  shut  off  by  a  IJ-in. 
handle  cock  at  the  branch  tee.  The  air  hose,  in  25  or  40-ft. 
lengths,  is  of  unwrapped  six-ply  rubber;  it  is  1J  in.  diameter,  the 
idea  being  to  preserve  from  the  level  main  a  minimum  section  of 
1  in.  diameter  through  IJ-in.  cock,  IJ-in.  hose  (which  is  choked 
on  mending  to  1  in.  inside  by  the  insertion  of  a  1-in.  nipple)  and 
IJ-in.  handle  cock  to  the  drill's  valve  chest. 

Tool  Sharpening.  —  The  blacksmith  shop  has  two  forges,  a 
drill  press  and  a  power  hammer  made  from  a  2J-in.  air  drill.  On 
each  shift  are  a  tool  sharpener  and  helper,  with  a  repair  black- 
smith and  helper  on  day  shift  besides.  Each  rock  drill  uses  from 
10  to  15  bits  per  shift,  which  are  in  sets  as  follows: 


Name 

Length 

Width 
(Cutting  Edge; 

Shape 

Starter  
2d 

2'  6" 
4'  6" 

2|" 
2i" 

\l"  star  alone. 
)  H"  star  bit; 

3d 

6'  6* 

If" 

(  1|"  octagon  shank. 
1^"  octagon  shank. 

4th 

8'  6" 

If" 

lj"  octagon  shank. 

5th 

10'  6V 

H" 

1  j  "  octagon  alone 

EXAMPLES  OF  ROCK   DRILL  PRACTICE  273 

The  starters  are  of  Vulcan  star  steel  swaged  down  at  one 
end  for  the  shank.  The  fifths  are  of  Vulcan  octagon  steel.  The 
seconds,  thirds,  and  fourths  have  each  a  star  steel  bit,  18  in. 
long,  split  at  one  end  for  welding  to  the  wedge-shaped  end  of  the 
octagon  steel  shank.  The  bits  are  draw-tempered  to  a  brown 
color  with  great  care  to  withstand  the  hardness  of  the  specular 
ore. 

WITHERBEE-SHERMAN  IRON  MINES,  NEW  YORK  l 

About  35  Ingersoll-Sergeant  drills  are  in  use  in  the  mines, 
operating  on  double  shifts.  These  are  of  the  2|-in.  size  and  put 
down  from  43  to  45  ft.  of  holes  per  man-day  (ten  hours).  They 
are  arranged,  on  account  of  the  character  of  the  ore  drilled,  to 
operate  at  a  higher  speed  and  on  a  shorter  stroke  than  is  usual, 
and  have  put  down  48  ft.  per  man-day  (average  of  one  month's 
run).  Hand-hammer  drills  of  the  "Little  Jap"  pattern  are  used 
to  some  extent  and  are  giving  satisfactory  results.  They  are 
operated  on  roof  work  and  block-holing. 

The  holes  average  about  8  ft.  in  depth;  they  are  not  drilled 
in  any  regular  order  and  each  hole  is,  to  all  intents  and  purposes, 
blown  out  by  itself.  They  are  all  fired  from  fuses,  for  the  reason 
that  a  series  of  holes  fired  by  electricity  is  found  to  give  pieces 
too  large  for  convenience  in  handling;  the  large  pieces  have  to  be 
broken  up  and  it  is  found  more  economical  and  less  arduous  to 
fire  individual  holes.  Of  course  the  firing  is  not  so  apt  to  pro- 
duce falls  of  roof  when  done  singly  as  when  a  number  of  holes 
are  fired  at  once,  nor  is  the  resulting  smoke  or  fume  nearly  so 
great  in  quantity. 

The  powder  generally  used  is  a  45  per  cent,  dynamite,  except 
in  cases  where  the  ventilation  is  not  so  perfect;  here  a  gelatine 
powder  of  the  same  strength  is  used. 

In  most  of  the  New  York  iron  mines,  an  air  pressure  of  60  lb., 
at  the  surface,  is  used. 

THE  DAVIS  PYRITES  MiNE,2  MASSACHUSETTS 

Character  of  Ore.  —  The  deposit  of  hard  pyrites  is  about  20  ft. 
thick  and  lies  between  a  foot-wall  of  mica-schist  and  a  hanging 
wall  of  quartzite. 

1  Eng.  and  Min.  Journ.,  June  2,  1905. 

2  J.  J.  Rutledge,  Eng.  and  Min.  Journ.,  Oct.  13  and  20,  1906. 


274 


ROCK   DRILLS 


The  ore  is  very  hard  and  the  crystals  are  firmly  bound 
together,  so  that  there  is  only  a  small  percentage  of  fines  made 
in  mining  the  ore. 

Sloping.  —  The  ore  is  mined  by  underhand  stoping,  Fig.  165. 
The  rise  is  driven  much  faster  than  the  winze,  but  as  all  holes 
(except  when  the  water  Leyner  drill  is  used)  are  dry  ones  the  work 
is  done  under  considerable  difficulty,  on  account  of  the  fine  dust 
filling  the  lungs  of  the  drillers.  The  Cover  respirator  was  used 
with  good  results  while  putting  up  a  raise  last  summer.  Such 
respirators  are  cheap  and  rather  effective. 


FIG.  165.  —  Underhand  stoping  system  (Davis  mine). 


After  the  winze  and  raise  are  connected  the  stope  is  opened 
up  by  taking  a  "bench"  down.  Usually  a  "12-hole"  bench  is 
started  by  drilling  12  holes  on  foot  and  hanging  walls,  about  2  ft. 
apart.  The  six  holes  nearest  the  winze  are  first  fired  and  the 
bench  split  in  that  way;  then  this  first  bench  is  carried  down  one 
step  in  advance  of  the  second  bench.  Usually  when  the  ore  is 
of  average  thickness  it  requires  one  month  to  take  down  a  12-ft. 
bench  from  top  to  bottom  of  the  stope.  Horizontal  floors  or 
jointing  planes  are  found  cutting  the  ore-body  at  distances  vary- 


EXAMPLES  OF  ROCK  DRILL  PRACTICE  275 

ing  from  2  to  9  ft.  apart  measured  vertically.  Holes  are  always 
drilled  nearly  to  these  floors  and  the  usual  depth  of  hole  is  from 
7  to  11  ft.  Long  holes  give  best  results.  The  distance  from 
collar  of  hole  to  edge  of  bench  varies  from  18  in.  to  2  ft.;  never 
more  than  2  ft.  A  hole  on  each  wall  is  always  necessary. 

National  dynamite  of  40  to  50  per  cent,  strength  is  employed 
on  the  stopes,  and  as  the  ore  to  be  merchantable  must  not  be  over 
powdered,  great  care  is  used  in  charging  the  holes. 

In  some  stopes  three  benches  are  carried  down  simultaneously, 
though  this  plan  usually  results  in  considerable  mucking  down  of 
the  ore  left  on  the  lower  benches  by  shots  from  the  upper  ones. 
When  this  plan  is  followed,  the  benches  are  found  to  be  from 
4  to  6  ft.  wide.  Rand  " Little  Giant"  No.  2  drills  are  used  in 
stoping,  one  runner  and  one  helper  being  employed  on  each  drill. 
The  helper  carries  his  own  steel  to  and  from  the  shaft. 

Hitches.  —  These  are  cut  by  hand  hammers  and  "points," 
which  latter  are  of  J-in.  steel,  sharpened  at  one  end,  somewhat 
in  the  manner  in  which  a  lead  pencil  is  sharpened.  Usually  two 
good  men,  one  holding  and  the  other  striking  the  point,  can  cut 
an  ordinary  hitch  in  a  shift,  or  at  most  a  shift  and  a  half.  Some 
progress  has  been  made  in  cutting  hitches  by  means  of  the  Little 
Wonder  hand  drill  and  special  hitch-cutting  tool  in  places  where 
the  foot-wall  is  not  too  hard.  Where  the  wall  is  hard,  nothing 
but  the  points  will  do  the  work. 

Back-Sloping  vs.  Underhand  Stoping  in  Large  Bodies  of  Iron 
Pyrites.  —  Theoretically,  in  mining  large  bodies  as  uniform  in 
nature  as  iron  pyrites  it  would  seem  that  the  overhand  or  back- 
stoping  method  would  be  most  economical,  and  yet  in  several 
large  iron-pyrites  mines  it  has  been  found  by  experience  that 
the  best  method  is  that  of  underhand  stoping,  Fig.  165.  A  con- 
sideration of  the  conditions  which  have  led  to  the  adoption  of 
the  underhand  method  may  not  be  out  of  place. 

Ordinarily,  when  back-stoping  has  been  the  method  of  mining 
employed,  it  has  been  necessary  to  drive  the  drift  above  the  stope 
in  order  to  open  it  up,  and  this  has  added  to  the  cost  of  -the  stoping 
as  well  as  delaying  the  rapid  opening  out  of  the  stope.  The  usual 
practice  is  to  use  stulls  in  mines  in  which  the  walls  require  support 
and  the  deposit  dips  at  a  high  angle,  and  to  allow  the  ore  and 
rock  to  fall  on  the  stulls  at  the  bottom  of  the  stope,  chutes  being 
used  to  load  the  ore  into  the  cars  in  the  level  below.  By  this 


276  ROCK  DRILLS 

method  gravity  assists  in  the  work  of  mining  and  less  powder 
is  necessary  to  break  the  ground  than  in  underhand  stoping. 
The  ore  is  separated  from  the  rock  on  the  stulls  and  the  rock 
left  to  support  the  walls,  instead  of  being  sent  to  the  surface. 
The  miners  usually  are  close  to  their  work  and  can  examine  the 
ground  overhead  at  all  times  and  pull  down  any  loose  pieces  of 
ore  or  rock. 

If  drills  are  placed  on  staging  made  usually  of  lagging  poles, 
instead  of  being  set  upon  the  loose  rock  and  ore  in  the  stope, 
there  is  always  vexatious  delay  in  cutting  hitches  for  the  lagging 
poles,  before  the  staging  can  be  erected.  The  spring  of  the  lag- 
ging, if  long,  bothers  the  driller  and  the  staging  often  falls,  endan- 
gering the  lives  of  the  driller  and  helper;  there  are  often  loose 
scales  of  pyrite,  sometimes  of  considerable  thickness,  which  must 
be  dislodged  before  the  staging  is  set  up,  or  before  any  work 
whatever  can  be  done  in  the  stope>  and  this  delay  of  necessity 
retards  all  other  work;  loose  pieces  of  ore  are  found  over  the  back 
of  the  drifts,  as  well  as  over  the  stopes,  and  become  very  dan- 
gerous, for  they  cannot  easily  be  detected,  as  the  ground  may 
be  solid  one  moment  and  the  next  a  dangerous  piece  of  ore  or 
rock  may  become  loosened  from  the  backs. 

All  holes  drilled  are  necessarily  dry  holes  and  must  be  care- 
fully tamped  and  fired  or  there  will  be  great  danger  from  sulphur 
fumes.  In  addition  to  the  foregoing  the  drillings  fall  down  upon 
the  drill  and  tend  to  shorten  its  life.  Drillers  and  timbermen, 
especially  those  inexperienced,  generally  dislike  to  trim  the  breasts 
and  walls  of  back-stopes,  or  to  prepare  for  and  erect  the  stagings, 
for  the  work  is  dangerous.  If  the  stope  is  wet  the  men  cannot 
as  easily  avoid  the  dropping  water  as  they  can  in  underhand  work. 

Machine  Drills.  —  In  the  stopes  the  Rand  " Little  Giant" 
No.  2  is  used  for  stoping.  This  drill  is  easily  hoisted  up  and 
down  the  stopes  by  means  of  the  cargo  winch  before  mentioned. 
Rand  drills  are  also  used  in  the  drifts  and  " Little  Giant"  No.  3 
is  used  in  the  sinking.  The  only  trouble  I  have  found  with  these 
drills  is  the  great  cost  for  repairs,  due  to  broken  pistons,  wornout 
feed-nuts,  chuck  bolts,  etc. 

McKiernan  drills  have  been  used  in  the  stopes  and  also  in 
the  drifts,  and  in  shafts  and  winze  work.  They  do  not  readily 
throw  the  mud  out  of  a  deep  hole  in  shafts  or  on  the  stopes,  prob- 
ably due  to  the  fact  that  the  moisture  in  the  air  freezes  in  them. 


EXAMPLES   OF  ROCK   DRILL  PRACTICE  277 

In  drifts,  rises,  and  in  all  dry  holes  the  McKiernan  gave  far  better 
results  than  the  Rand.  A  Leyner  water  drill  has  been  used  in 
drifting  with  good  results  when  in  the  hands  of  a  careful  runner. 
On  account  of  the  difficulty  in  carrying  water  to  the  Leyner  in  the 
stopes,  it  did  not  give  very  satisfactory  results.  However,  water 
could  be  brought  from  the  shaft  column  pipe  for  use  with  drills 
(Davis  mine  water  is  extremely  acid,  and  generally  eats  metal  sur- 
faces very  rapidly)  and  by  using  Leyners  in  stoping,  one  helper 
could  be  dispensed  with ;  as  the  two  drills  are  usually  side  by  side, 
two  runners  and  one  helper  could  easily  operate  two  drills.  Most 
of  the  helper's  duty  at  present  on  the  Leyner  consists  in  carrying 
water  to  the  tanks  and  assisting  in  jacking  bar,  setting  tripod,  or 
changing  bits.  Another  good  feature  of  this  drill  is  that  dry  holes 
never  result  from  its  use.  This  drill  creates  no  dust  when  used 
in  rising  or  drifting  and  removes  a  very  disagreeable  accompani- 
ment of  such  work  when  performed  with  other  drills.  Among 
the  disadvantages  connected  with  the  use  of  the  water  Leyner 
are  the  complicated  nature  of  the  machine,  and  the  necessity  for 
the  employment  of  a  competent,  skilled  runner,  the  greater  skill 
necessary  to  sharpen  the  drills,  the  necessity  for  having  a  uni- 
formly high  air  pressure  in  order  to  obtain  the  best  results,  and 
frequent  breakage  of  chucks. 

Little  Wonder  air  hammer  drills  and  Little  Jap  hammer  drills 
are  used  for  block  holing  and,  where  the  foot- wall  is  soft  enough, 
for  hitch  cutting.  For  the  latter  purpose  a  special  hitch-cutting 
tool  is  employed.  Both  these  drills  give  considerable  annoyance 
at  times,  through  the  sticking  of  the  hammer.  The  Little  Wonder 
gave  most  satisfactory  results.  At  one  time  the  stopes  were  kept 
going  two  weeks  by  the  use  of  the  Little  Wonder  drills  alone 
by  drilling  4-ft.  holes,  while  the  Rand  stope  drills  were  being 
overhauled.  Both  the  Little  Winder  and  the  Little  Jap  drill 
the  pyrites  easily  and  cheaply,  but  refuse  to  cut  the  hard  foot 
or  hanging.  They  do  not  work  well  in  wet  ground.  Generally 
the  greatest  source  of  trouble  connected  with  their  use,  aside 
from  the  sticking  of  the  hammer,  was  the  bending  or  breaking 
of  the  hollow  bits  at  the  point  where  the  steel  shank  or  point 
was  welded  or  brazed  to  the  stay-bolt  iron  constituting  the 
body  of  the  drill.  This  difficulty  has  been  lessened  through  the 
employment  of  a  solid  bit  of  hexagonal  steel,  which  has  a  f-in. 
hole  drilled  lengthwise  through  it.  These  bits  will  not  bend,  do 


278  ROCK    DRILLS 

not  require  tempering  of  shank  or  points,  and  can  be  sharpened 
like  the  steel  used  in  the  large  drills,  and  do  not  require  careful 
handling.  Their  use  is  a  decided  improvement  over  the  soldered 
or  brazed  bits.  Although  the  dust  from  the  small  air  drills  is 
annoying,  their  use  results  in  such  a  great  saving  over  hand  drills 
that  they  are  generally  used  for  block  holing  and  trimming  ore  on 
foot  and  hanging.  A  1-in.  air  pipe  is  run  along  behind  the 
muckers,  and  they  can  use  the  hand  drills  themselves  whenever 
necessary.  The  hand  drills  cannot  drill  wet  ground. 

Shaft  Sinking.  —  Rand  "Little  Giants"  No.  3  are  used  in 
sinking.  From  25  to  30  ft.  of  holes  is  a  fair  shift's  work  in 
drilling.  Usually  four  cuts  are  taken  out  per  month.  These 
cuts  vary  in  depth  from  5  to  7  ft.  The  shaft  is  9  X  18  ft.  out- 
side the  timbers.  Experience  has  shown  that  the  V  cut  gives 
the  best  results  when  placed  as  shown  in  the  accompanying 
drawing,  Fig.  165. 

Sometimes  it  is  necessary  only  to  drill  four  holes  in  a  round, 
but  usually  five  holes  are  required  to  pull  the  ground.  A  60 
per  cent,  powder  is  used  to  pull  the  V  cut  (No.  1  and  No.  2  rounds), 
and  40  per  cent,  powder  is  used  on  No.  3  and  No.  4,  as  it  has 
been  found  that  the  shaft  is  more  quickly  mucked  when  lumps 
are  made,  rather  than  fine  ore.  No.  3  and  No.  4  on  one  end  are 
fired  and  entirely  mucked  before  the  No.  3  and  No.  4  of  the  other 
end  are  fired;  and  if  No.  1  and  No.  2  break  well,  No.  3  and  No.  4 
on  each  end  merely  break  like  stope  holes  and  yield  large  lumps 
with  consequent  easy  mucking  and  rapid  hoisting.  An  average 
rate  of  progress  is  about  20  to  30  ft.  per  month. 

Blasting.  —  In  the  Davis  pyrites  mine  it  will  be  noted  that 
blasting  practice  is  regulated  by  the  necessity  of  preparing  the 
pyrites  in  lump  size  for  the  market.  Holes  are  not  loaded  with 
the  maximum  charge,  nor  fired  with  the  maximum  burden. 

PORTLAND  GOLD  MINING  COMPANY,  CRIPPLE  CREEK,  COLO. 

A  discussion  of  the  relative  merits  of  the  large  3|-in.  machine 
and  the  small  2J-in.  machine  by  Frederick  T.  Williams,1  gives 
the  following  particulars  of  costs  and  methods  employed  by  the 
Portland  Gold  Mining  Company. 

Large  vs.  Small  Drilling-Machines.  —  The  headings  here 
described  wrere  driven  through  highly  indurated,  andesitic  breccia, 
1  Bull  No.  8,  Mar.  1906,  Am.  Inst.  Min.  Eng. 


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280  ROCK  DRILLS 

having  a  hardness  of  from  5.2  to  7.2  and  a  sp.  gr.  of  from  2.2  to 
2.8.  The  action  of  the  breccia  under  the  drill  was  not  materially 
different  from  that  of  ordinary  red  granite.  The  breccia  was 
not  as  free-drilling  as  granite,  and  sludge  accumulated  very 
rapidly  after  a  shallow  depth  of  hole  had  been  gained,  but  it 
broke  better  than  granite. 

Aside  from  the  usual  work  of  setting  up,  drilling,  and  loading, 
the  machine-men  or  helpers  mucked  back,  cleaning  the  floor  of 
muck  3  or  4  ft.  back  from  the  breast  in  order  to  position  the 
column  properly.  If  the  "lifters"  acted  properly  at  the  previous 
firing,  the  muck  was  fairly  well  thrown  back  from  the  breast; 
but  if  either  missed  fire  or  were  exploded  before  the  other  holes, 
considerable  muck  was  left  at  the  breast  which  required  much 
additional  labor.  The  usual  time  needed  to  muck  back  was 
1.25  hour,  but  this  varied  considerably.  Flat  steel  48  X  96  X  f- 
in.  sheets  were  used,  from  which  to  shovel  the  material.  These 
were  placed  in  position  3  or  4  ft.  back  from  the  breast  by  the 
trammer  just  before  going  off  shift.  The  ground  broke  fine 
enough  to  require  little  or  no  sledging.  A  cubic  foot  of  breccia 
in  place  will  average  154  Ib.  in  weight  as  compared  with  90  Ib. 
on  the  muck-pile,  giving  an  average  of  42  per  cent,  of  void  space. 
All  the  waste  was  trammed  to  the  shaft  800  ft.  distant,  and  hoisted 
to  the  surface.  No  timber  was  used  in  either  heading. 

The  following  summary  of  the  results  obtained  by  using  both 
large  and  small  machines  has  been  prepared  from  the  data  given 
in  Tables  1  and  2.  Labor  is  the  largest  individual  item.  The 
wages  of  machine-men  were  $4  per  shift,  and  the  addition  of  the 
items  given  under  the  several  heads  of  Table  I  shows  the  total 
cost  of  labor  performed  in  each  heading.  The  cost  of  operating 
the  machines  per  shift  was  $3.70  for  the  large  machine  and  $1.85 
for  the  small  machine;  these  figures,  which  vary  from  month  to 
month,  include  the  cost  of  everything  connected  with  the  opera- 
tion of  the  machines :  engineer's  wages,  blacksmith  expense,  new 
steel,  repairs  to  the  machines,  cost  and  repair  of  air-lines,  etc. 
The  cost  of  labor,  per  foot  driven,  by  the  large  machine  was  $3.45, 
and  by  small  machine  $2.56. 

The  cost  of  explosives,  a  detailed  report  of  which  is  given  in 
Table  II,  shows  that  the  40-per  cent,  dynamite  costs  $0.127  per 
Ib.,  the  fuse,  $0.0035  per  ft.;  and  the  caps,  $0.007  each. 

These  figures,  which  include  freight,  unloading,  wages  of  the 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


281 


TABLE  II.     EXPLOSIVES  —  DETAILED    REPORT     OF   THE    PORTLAND    GOLD 
MINING  COMPANY  FOR  20  DAYS,  ENDING  OCTOBER  16,  1903 


Lb.of 
Powder 

Lb.  of 
Powder 
per  Foot 
Driven 

Feet  of 
Fuse 

Feet  of 
Fuse  per 
Foot 
Driven 

Number 
of  Caps 

Number 
of  Caps 
per  Foot 
Driven 

Large  machine  (3|"). 
Cross-cut  (5.5'  X  7.5'). 
5-day  run 

491 

1723 

872 

30  59 

116 

407 

8-day  run  
7-day  run  . 

669 
544 

14.39 
15.32 

1,179 
804 

25.35 
2265 

158 
134 

3.39 

3  77 

Averages  and  totals.  .  . 

1,704 

15.40 

2,855 

25.80 

408 

3.69 

Small  machine  (2f"). 
Cross-cut  (4.5'  X  7'). 
5-day  run 

264 

11.00 

672 

2800 

96 

400 

8-day  run  
7~day  run  

378 
262 

9.45 

7.82 

1,129 
742 

28.22 
22.15 

151 
120 

3.77 
3.58 

Averages  and  totals  .  .  . 

904 

9.27 

2,543 

26.08 

367 

3.76 

powder-man,  and  one  third  of  the  wages  of  the  storekeeper, 
represent  the  entire  cost  of  the  material,  as  laid  down  at  the 
station  for  the  machine  men.  All  fuse  burned  was  in  7-ft.  lengths. 
The  number  of  feet  of  fuse  burned  and  the  number  of  caps  used 
per  foot  are  practically  the  same;  but  the  cost  of  dynamite  is 
$0.78  less  per  foot  in  the  heading  driven  by  the  small  machine 
than  in  that  of  the  large  machine. 

The  best  record  for  a  shift's  run,  made  by  the  large  machine, 
was  4.08  ft.,  as  compared  with  2.96  ft.  for  the  small  machine. 
In  drilling  these  rounds  it  was  found  that  the  large  machine  had 
made  3109.56  cu.  in.  of  hole,  and  the  small  machine  971.10  cu.  in. 
Comparing  these  figures  with  the  cubic  feet  of  ground  pulled, 
1  cu.  in.  of  hole  drilled  by  the  large  machine  broke  0.053  cu.  ft. 
of  breast,  while  the  small  machine  gave  0.097  cu.  ft.  This  com- 
parison shows  that  too  much  work  was  done  by  the  big  machine 
on  the  breast  for  the  amount  of  ground  broken. 

•Figs.  167  and  168  show  the  number  of  holes  drilled,  the 
degrees  of  pitch  from  the  horizontal,  the  depth  drilled  by  the 
starters,  seconds  and  thirds,  and  the  order  of  firing.  The  cost 
of  coal  before  the  boilers  was  $4.40  per  ton.  Ordinary  cross  or 


282 


ROCK   DRILLS 


4-50 

"FRONT  ELEVATION 


SIDE  ELEVATION 


FIG.  167.  —  Arrangement  of  holes  for  2-inch  drill,  Portland  G.  M.  Co. 
Cripple  Creek. 


^xvZ'&Z%§$%%§> 
— fcSO-1- — 

FBONT  ELEVATION  SIDE  ELEVATION 

Fio.  168.  —  Arrangement  of  holes  for  3}-inch  drill,  Portland  Gold  Mining  Co. 


EXAMPLES  OF  ROCK   DRILL  PRACTICE  283 

square  bits  were  used,  and  all  the  steel  was  sharpened  by  machine. 
At  each  sharpening  the  steel  lost  J  to  f  in.  in  length.  The  general 
tramming  cost  includes  repairs  to  tram-cars,  tram-tracks  and  the 
greasing  of  the  cars. 

The  cost  of  pipe  and  track  is  figured  at  $0.41  per  ft.,  the  2-in. 
pipe  costing,  with  connections,  $0.10  per  ft.,  the  track,  together 
with  the  spikes,  plates,  and  ties,  costing  $0.31  per  ft.  Lumber 
costs  $20  per  thousand  feet. 

Hoisting  cost  $0.243  per  ton,  which  includes  all  accounts  that 
can  be  charged  to  the  maintenance  of  the  hoisting  engines  —  such 
as  wages  of  the  engineers,  wipers,  top-men  and  cagers,  repairs, 
cost  of  steam,  cables,  and  repairs  to  shaft.  The  hoist  used  is  a 
500-h.p.  Webster,  Camp  &  Lane,  first-motion  hoist,  size  20  X  48 
in.,  having  a  capacity  for  a  maximum  depth  of  2500  ft.,  using 
5  X  | -in.  rope  to  hoist  an  unbalanced  load  of  8000  Ib.  at  an  aver- 
age speed  of  1500  ft.  per  minute. 

To  supplies  is  charged  the  cost  of  picks  and  shovels.  To 
general  expense  is  charged  the  wages  of  foremen  and  shift  bosses, 
assaying  and  surveying,  pumping,  lighting,  including  candles, 
office  expense,  and  general  repairs  on  the  surface.  The  air  pres- 
sure at  the  receiver  was  100  Ib.  and  at  the  drills  85  Ib.  per  square 
inch. 

The  bore  of  the  large  machine  cross-cut  is  5.5  X  7.5  ft.,  that 
of  the  small  machine  is  4.5  X  7  ft.;  it  is  held  that  the  increase  of 
1  ft.  in  width  and  0.5  ft.  in  hight  of  the  large  machine  cross-cut 
over  that  of  the  small  machine  cross-cut  does  not  facilitate  mining 
operations. 

The  merits  of  the  work  done  by  the  two  machines  may  be 
briefly  stated  thus:  The  use  of  the  small  machine  saves  25  per 
cent,  of  the  cost  of  labor  necessary  to  operate  a  large  machine 
foot  per  foot.  The  cost  of  operating  a  small  machine  is  50  per 
cent,  less  than  that  of  operating  a  large  machine,  shift  for  shift. 
The  general  tramming  cost  of  the  large  machine  cross-cut  is 
lessened  20  per  cent,  by  using  a  small  machine.  The  cost  of 
explosives  per  foot  driven  by  the  large  machine  can  be  reduced 
37.7  per  cent,  by  the  use  of  the  small  machine.  The  cost  of 
hoisting  and  general  expense  of  the  large  machine  cross-cut  is 
lessened  nearly  20  per  cent,  by  using  the  small  machine. 

Greater  speed,  regardless  of  cost,  can  be  obtained  with  the 
large  machine,  the  small  machine  being  from  10  to  20  per  cent. 


284  ROCK  DRILLS 

slower.     The  cost  of  the  large  machine  cross-cut  was  reduced 
27  per  cent,  by  using  the  small  machine. 

We  have  here  in  Mr.  Williams'  discussion  an  example  of  the 
use  of  the  drag  cut  instead  of  center  cut,  and  of  40  per  cent, 
dynamite  instead  of  blasting  gelatine  used  on  the  Rand.  The 
cost  and  efficiency  of  the  labor  employed  also  governs  the  way 
in  which  the  work  is  carried  out.  Extreme  speed  is  not  necessary 
and  one  man  can  be  made  to  operate  a  2J-in.  machine  as  compared 
with  one  man,  and  five  natives  for  two  machines  on  the  Rand. 
The  ground  breaks  with  fewer  holes.  Such  an  arrangement  of 
holes  as  shown  in  Figs.  167  and  168  would  not  break  a  really 
tight  face,  but  is  most  economical  in  boring  and  in  the  use  of 
explosives  in  the  case  given.  Air  pressures  at  Cripple  Creek  are 
85  Ib.  at  the  machines. 

CENTER  STAR  MINE,  ROSSLAND,  B.  C. 

Large  Machines  for  Stoping.1  —  There  are  36  air  drills  employed 
in  the  mine,  most  of  which  are  3f  in.  Rand  machines.  Of  these 
drills  10  to  16  are  constantly  employed  on  development  work. 
In  the  stopes  a  pair  of  miners,  with  one  machine,  will  drill  from 
30  to  40  ft.  of  holes  in  an  8-hour  shift,  30  ft.  being  the  rule.  The 
holes  are  from  6  to  8  ft.  deep,  the  longest  steel  in  use  being  10 
ft.  in  length.  Each  drill  in  the  stopes  averages  from  20  to  30 
tons  of  broken  ore  in  the  two  8-hour  shifts. 

From  1200  to  1600  ft.  of  development  work  are  done  each 
month.  In  a  drift  6  X  9  ft.  in  the  clear,  the  monthly  advance 
is  from  120  to  180  ft.,  the  latter  figure  being  the  record.  The 
round  consists  of  10  holes  5  to  6  ft.  deep,  which  advances  the  drift 
from  4  2  to  5  ft.  A  round  is  usually  drilled  in  two  shifts. 

The  Center  Star  group  of  mines  employs  about  425  men, 
who  average  a  little  better  than  li  tons  of  ore  broken  per  man. 
Two  8-hour  shifts  are  worked,  the  first  crew  going  underground 
at  7  a.m.,  and  the  second  at  3  p.m.  The  change  is  made  under- 
ground at  the  work.  At  11  p.m.  a  crew  of  four  blasters  for  each 
mine  goes  on,  and  these  men  load  and  blast  all  the  holes  drilled 
during  the  previous  two  shifts.  Any  missed  holes  are  reported 
and  listed  on  a  blackboard  in  the  shaft  house.  This  system  has 
greatly  reduced  the  number  of  accidents,  and  also  makes  it  pos- 
sible for  the  miners  to  work  in  good  air;  for  there  is  ample  time 
1Eng.  and  Min.  Journ.,  Jan.  1,  1910. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


285 


for  the  slopes  and  drifts  to  become  cleared  of  powder  smoke  and 
gas  before  the  day  shift  comes  on. 

FINDLEY  CONSOLIDATED  GOLD  MINING  COMPANY,  CRIPPLE 
CREEK,  COLORADO 

Sloping.  —  Hammer  drills  of  the  types  already  discussed  Have 
largely  displaced  piston  drills  for  stoping,  and  are  also  used  for 
sinking,  raising,  and  drifting.  G.  E.  Wolcott 1  gives  the  following 
description  of  stoping  as  done  by  the  Findley  Consolidated  Gold 
Mining  Company. 

The  machine  used  is  surmounted  with  the  air-feed  attachment. 
The  method  of  stoping  is  the  ordinary  filled  stope  system  as 
represented  in  Fig.  169.  The  ore  is  drawn  out  from  the  stopes 
so  as  to  leave  a  working  space  of  from  6  to  8  ft.  between  the 


FIG.  169.  —  Method  of  stoping  in  Findley  Consolidated  mine. 

broken  rock  and  the  roof.  In  starting  to  drill  all  that  is  neces- 
sary is  to  lay  a  short  plank  on  top  of  the  muck  pile,  place  the 
point  of  the  air-feed  upon  this  and  start  the  machine.  In  prac- 
tice it  is  easy  to  begin  drilling  in  less  than  15  minutes  after  enter- 
ing the  stope,  all  that  is  necessary  being  to  bring  the  machine  to 
place  and  connect  the  hose.  A  plank  to  stand  the  air-feed  upon 
is  not  even  necessary,  as  when  the  broken  rock  lies  rather  close 
to  the  roof  the  end  of  the  air-feed  can  be  thrust  into  the  muck 
pile  and  drilling  carried  on  as  well  as  with  a  plank  to  rest  upon. 

HOT-TIME  LATERAL  OF  THE  NEWHOUSE  TUNNEL,  COLORADO 

The  adit 2  was  driven  through  granite,  gneiss,  and  schist,  very 
hard  to  drill  and  so  tough  and  tenacious  that  it  broke  badly. 
There  were  no  soft  seams  nor  any  defined  walls  to  follow.  The 

1  Eng.  and  Min.  Journ.,  July  20,  1907. 
2Eng.  and  Min.  Journ.,  Oct.  17,  1908. 


286  ROCK  DRILLS 

fact  that  there  was  no  timbering  to  be  done;  that  the  ground  was 
not  wet  enough  to  require  rubber  coats;  and  that  the  size  of  the 
bore,  5  X  7?  ft.  in  the  clear  above  the  rails,  corresponded  so 
closely  with  the  usual  size  of  mine  workings  made  the  problem, 
in  all  essential  conditions,  the  counterpart  of  the  problem  hun- 
dreds of  properties  are  working  on  every  day. 

The  machine-man  and  helper  set  up  the  drill  without  waiting 
for  the  dirt  from  the  previous  shots  to  be  cleaned  up.  The  set-up 
was  on  a  cross-bar  placed  high  enough  in  the  drift  and  far  enough 
away  from  the  face  to  allow  the  upper  row  of  holes  to  be  started 
close  to  the  back  and  to  be  drilled  with  very  little  rise  in  their 
depth  of  6  ft.  The  usual  round  was  15  holes,  each  6  ft.  or  more 
deep  and  having  a  diameter  of  li  in.  at  the  bottom.  When  the 
ground  showed  any  peculiarities  which  indicated  that  another 
hole  or  two  would  be  necessary  in  order  to  break  the  ground 
well  these  were  drilled  where  needed.  The  ordinary  round  con- 
tained 90  ft.  of  drill  holes,  so  that  to  make  the  set-ups,  drill  the 
round,  tear  down,  load  and  shoot  the  holes  required  the  full 
8-hour  shift.  Each  round  broke  from  4  to  4J  ft. 

Mr.  Knowles  used  the  Model  6,  Water-Ley ner  drill.  The  use 
of  hollow  steel  flushed  with  a  stream  of  water  made  it  possible 
to  keep  the  bottom  of  the  hole  clear  of  cuttings,  and  the  bit  cool, 
so  that  each  blow  is  struck  full  on  the  clean  face  of  the  rock. 
By  using  this  drill  the  crew  gained  the  time  usually  lost  in  scrap- 
ing the  hole,  and  in  changing  the  steel  frequently.  The  saving 
of  this  lost  time,  which  in  the  aggregate  consumes  a  large  part 
of  the  drilling  period,  is  one  of  the  most  important  features  of 
this  work,  and  one  to  which  Mr.  Knowles  ascribes  a  large  part 
of  his  success. 

OPHELIA  TUNNEL,  CRIPPLE  CREEK,  COLORADO 

W.  P.  J.  Dinsmore  in  Mine  and  Quarry  gives  particulars  of 
the  work  of  driving  the  Ophelia  Tunnel.  The  tunnel  was  driven 
straight  8500  ft.,  and  was  about  9X9  ft.  in  the  clear.  It  pierced 
granite  and  breccia  with  dikes  of  phonolite,  andesite,  and  nepha- 
line.  The  rate  of  advance  was  350  to  375  ft.  per  month.  In 
one  month  395J  ft.  were  driven.  Two  Sullivan  UE-Z,  3J-in. 
drills  were  employed,  three  8-hour  shifts.  The  number  of  men 
per  shift  was  seven,  consisting  of  two  machine  drill  men,  two 
helpers,  and  three  muckers  or  " clean-up  men."  Each  shift  was 


EXAMPLES   OF  ROCK  DRILL  PRACTICE  287 

to  drill,  load,  and  shoot  a  round  of  from  18  to  22  holes,  drilled 
5|  to  7  ft.  deep,  as  well  as  to  load  broken  rock  from  preceding 
blast  and  deliver  it  to  the  end  of  haulage  line. 

The  method  pursued  was  essentially  as  follows: 1 
11  As  soon  as  the  smoke  resulting  from  the  shooting  done  by  the 
previous  shift  was  cleared,  the  new  shift  of  drill  men,  helpers,  nand 
'muckers'  all  went  to  work,  and  the  broken  rock  from  the  face 
was  thrown  back  sufficiently  to  allow  the  columns  for  mounting 
the  drills  to  be  put  in  place.  The  two  drill  men  worked  together, 
and  the  two  helpers  worked  together  in  pairs,  relieving  each  other 
at  intervals;  the  'muckers'  going  immediately  to  work,  getting 
the  'muck'  into  the  cars  and  on  its  way  to  the  dump.  When 
the  helpers  were  working  on  the  muck  pile,  the  drill  men  were 
back  of  the  work;  looking  up  equipment;  seeing  that  all  the 
machine  drills,  steel,  hose,  tools,  blocking,  etc.,  that  would  be 
required  for  the  shift's  work  were  on  hand,  and,  if  anything  was 
found  missing,  taking  steps  to  secure  it.  When  the  drill  men 
were  working  on  the  muck  pile,  the  helpers  were  employed  in 
bringing  the  required  material  up  to  the  face,  where  it  would  be 
readily  available. 

"Muck  as  Staging.  —  In  clearing  away  the  muck,  care  was 
taken  that  it  should  not  fall  back  toward  the  face  until  a  sufficient 
space  was  provided  in  which  to  set  the  columns.  After  the  col- 
umns were  set  the  muck  was  allowed,  and  in  fact  encouraged  to 
fall  back,  until  it  had  filled  the  space  in  front  of  the  face  up  to 
such  a  level  that  the  tops  of  the  jack  screws  of  the  columns  could 
just  be  reached.  By  this  method  the  back  holes,  or  those  nearest 
the  top  of  the  tunnel,  were  the  first  to  be  drilled,  and  the  drill 
men  and  helpers  worked  from  the  top  of  the  muck  pile.  This 
did  away  with  any  form  of  staging,  and  while  the  drill  men  worked 
toward  the  bottom  of  the  tunnel,  the  helpers  were  removing  the 
pile,  Fig.  170,  thus  always  giving  the  drill  men  standing  ground 
of  proper  hight,  or  really  a  self-adjusting  platform,  much  wider 
and  more  solid  than  any  portable  timber  staging.  It  was,  of 
course,  necessary  for  the  muckers  to  finish  loading  out  the  muck 
before  the  drill  men  reached  the  bottom  holes  or  'lifters,'  but 
they  did  not  stop  work  until  the  end  of  the  shift  was  reached,  as 
there  was  rail  laying,  and  the  placing  of  sheets,  to  occupy  their 
attention  until  the  holes  were  loaded  and  ready  for  shooting. 
1  Mine  and  Quarry. 


288 


ROCK   DRILLS 


"Arrangement  of  Drill  Holes. — The  important  matter  of  prop- 
erly placing  and  shooting  drill  holes  was  carried  on  as  follows: 
In  Fig.  171,  holes  Nos.  1  and  2  are  cut  holes.  These  were  drilled 
from  6  to  7  ft.  deep,  looking  down,  and  were  so  placed  and  directed 


FIG.  170.  —  Drilling  and  mucking  in  face  of  Ophelia  tunnel. 

that  their  inner  ends  nearly  met.  The  fuse  for  these  holes  was 
so  cut  that  they  were  fired  first  and  nearly  at  the  same  moment. 
Holes  Nos.  3  and  4  are  cut  holes,  drilled  looking  up  and  about 
the  same  depth  as  Nos.  1  and  2.  They  were  so  directed  that 
their  inner  ends  did  not  meet,  as  in  the  case  of  Nos.  1  and  2. 


FIG.  171.  —  Arrangement  of  holes  for  heading  in  hard  ground,  Ophelia  tunnel. 

The  fuse  was  so  adjusted  that  these  holes  were  fired  just  after 
Nos.  1  and  2.  Holes  Nos.  5  and  6  are  the  back  cut  holes.  They 
were  drilled  looking  up,  and  so  directed  that  their  inner  ends  did 
not  meet,  nor  did  they  extend  beyond  the  top  of  the  tunnel. 
These  holes  were  shot  together  and  just  after  Nos.  3  and  4.  Cut 


EXAMPLES  OF  ROCK  DRILL    PRACTICE  289 

holes  Nos.  7  and  8  look  down,  and  were  timed  to  shoot  after 
Nos.  5  and  6.  'Holes  Nos.  9  and  10,  the  cut  lifters,  look  down 
and  extend  below  the  proposed  bottom  of  the  tunnel.  Holes 
Nos.  11  and  12,  the  back  rib  holes,  and  holes  Nos.  13  and  14, 
rib  holes,  look  up.  Holes  Nos.  15  and  16,  also  Nos.  17  and  18, 
rib  holes,  and  holes  Nos.  19^  and  20,  rib  lifters,  all  look  down  "and 
all  extend  beyond  the  line  of  the  side  walls,  and  were  all  shot  at 
nearly  the  same  time. 

"  Where  stiff  ground  was  encountered  holes  A  and  B  were  put 
in,  and  shot  with  holes  Nos.  1  and  2  and  Nos.  7  and  8  respectively. 
Where  very  difficult  ground  was  found,  holes  C  and  D  were  added 
and  shot  with  holes  Nos.  5  and  6  and  Nos.  3  and  4  respectively. 
By  analyzing  the  above  it  will  be  found  that  holes  Nos.  1  and  2 
take  out  or  loosen  a  wedge-shaped  portion  of  the  rock,  thus  reliev- 
ing the  resistance  to  the  action  of  the  powder  in  holes  Nos.  3  and 
4  and  holes  Nos.  7  and  8.  Holes  Nos.  3  and  4  and  Nos.  7  and  8 
clear  the  way  for  holes  Nos.  5  and  6  and  Nos.  9  and  10.  Holes 
Nos.  9  and  10  have  a  tendency  to  throw  any  broken  rock  above 
them  out  of  the  way  of  the  remaining  rib  holes.  Holes  A,  B,  C, 
and  D  serve  simply  to  increase  the  effect  of  the  holes  with  which 
they  are  shot.  By  placing  the  holes  in  this  way  and  shooting 
in  this  order,  the  break,  with  very  few  exceptions,  always  cleared 
the  rock  for  the  full  width  and  depth  of  the  tunnel,  thus  doing 
away  with  the  necessity  of  following  the  heading  with  any  work 
designed  to  break  off  projections. 

"  Tamping  material  for  use  in  the  loading  of  the  holes  was 
always  employed.  It  was  found  that  by  using  this,  the  re- 
sults obtained  were  most  satisfactory,  and  that  less  solder  was 
consumed. 

"Handling  the  Muck.  —  Two  tracks  were  maintained  close  to 
the  heading.  Before  the  shots  were  fired,  steel  sheets  were  placed 
on  the  floor  close  to  the  face,  extending  back  far  enough  to  receive 
all  the  broken  rock.  It  was  found  important  to  have  these  sheets 
weighted,  and  enough  muck  was  kept  on  at  the  face  to  do  this 
properly.  The  sheets  formed  a  smooth  floor  from  which  to 
shovel  the  muck,  but  unless  the  sheets  were  weighted,  it  was 
found  that  the  vacuum,  created  by  heavy  shot,  was  likely  to 
lift  them  and  mix  them  with  the  muck,  thus  not  only  defeating 
the  purpose  for  which  they  were  intended,  but  actually  increasing 
the  labor  of  mucking.  The  sheets  behind  the  main  portion  of  the 


290  ROCK  DRILLS 

muck  pile  served  to  receive  part  of  the  muck  thrown  from  the 
face,  and  also  to  facilitate  the  handling  of  cars." 

It  will  be  noticed,  in  the  Ophelia  tunnel,  that  the  wide  face 
open  to  attack  by  drill  holes  enables  the  center  3  or  4  hole  cut 
to  be  avoided;  several  holes  of  a  " breaking  in"  character  form  a 
"  square  center  cut."  The  difference  in  the  rate  of  drilling  com- 
pared with  that  attained  in  South  Africa  is  obvious.  Two 
machines  bore  18  to  20  holes  in  5  or  6  hours;  in  South  Africa 
three  machines  of  larger  diameter  take  about  8  hours  to  bore  15 
holes. 

ROOSEVELT  DRAINAGE  TUNNEL,  CRIPPLE  CREEK,  COLORADO  l 

The  country  rock  through  which  the  Roosevelt  drainage  tun- 
nel in  the  Cripple  Creek  district  has  already  been  driven  more 
than  two  miles  is  entirely  of  biotite-granite  gneiss.  The  abun- 
dance of  biotite  (black  mica)  in  the  rock  renders  the  granite  elas- 
tic, and  this  elasticity  interferes  with  the  breaking  of  the  rock. 
The  method  of  overcoming  this  difficulty  is  to  increase  the  per 
cent,  of  nitroglycerine  in  the  blasting  powder,  and  also  to  add  gun 
cotton.  Such  an  explosive  shatters  the  rock  much  more  effect- 
ively than  the  ordinary  dynamite  used  in  mining.  A.  S.  Pearce, 
the  superintendent,  used  powder  composed  of  92  per  cent,  nitro- 
glycerine and  8  per  cent,  gun  cotton.  This  compound  he  found 
the  most  satisfactory  explosive  for  gneissoid  granite.  This  ex- 
plosive is  used  in  the  center  cuts  while  lower-grade  powder,  some 
containing  40,  some  50,  and  some  60  per  cent,  of  nitroglycerine, 
is  used  for  the  balance  of  the  ground. 

The  tunnel  is  10  ft.  wide  and  6  ft.  high,  with  the  roof  and  sides 
well  squared  up  throughout. 

Leyner  drills,  No.  6,  were  used  and  found  satisfactory;  they 
drill  rapidly  and  do  not  get  out  of  order  readily.  The  holes  are 
2J  in.  in  diameter  at  the  collar  and  1J  in.  at  the  bottom;  the  depth 
is  from  7  to  9  ft.  Two  men  are  required  to  run  each  large  machine 
used  in  the  heading,  and  three  8-hour  shifts  are  employed. 

Twenty-six  holes  are  drilled  and  these  are  so  directed  and 
fired  that  much  of  the  waste  is  thrown  to  one  side  as  it  breaks, 
greatly  facilitating  its  quick  removal  while  the  next  shift  is  com- 
mencing operations. 

Mr.  Pearce  states  that  his  average  during  10  months  was 
1Eng.  and  Min.  Journ,,  Nov.  27,  1909. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


291 


361  ft.,  4  in.  per  month.  During  the  month  of  August  he  made 
410  ft.  This  distance  was  drilled  in  spite  of  the  fact  that  he  lost 
56  hours  from  the  disabling  of  the  electric  plant,  through  wash- 
outs down  the  creek.  In  September,  with  a  loss  of  108  hours,  he 
drove  the  heading  399  ft. 

ROCK  DRILLS  IN  TUNNELS  IN  EUROPE  AND  AMERICA 

The  following  particulars  have  been  taken  from  an  article 
by  R.  L.  Herrick  in  Miners  and  Minerals,  April,  1909,  and  from 
later  data  collected  by  myself.  Sullivan  machines  were  used  in 
the  Ophelia  and  Gunnison  tunnels;  Leyner  drills  in  Hot-Time 
Lateral  and  Elizabeth  Lake  tunnels. 

The  Brandt  rotary  drill  was  employed  in  the  Simplon  tunnel, 
putting  in  holes  33  in.  deep,  3?  in.  in  diameter.  The  Ferioux 
percussion  drill  drove  the  Arlberg  tunnel. 

The  Ingersoll-Sergeant  auxiliary  valve  drill  (3f  in.  diam.), 
using  from  drills  on  a  carriage,  drove  the  Loetschberg  tunnel, 
putting  in  12  to  14  holes,  4  ft.  deep,  2  in.  diameter  at  the  bottom, 
in  60  minutes. 

Generally  the  European  practice  has  been  to  drill  slant  holes 
of  large  diameter  and  to  blast  often,  while  the  American  practice 
has  been  to  drill  longer  holes  and  to  blast  seldom.  The  advance 
for  one  round  in  Europe  would  be  3  to  4  ft.,  and  in  America  4?  to 
7  ft.  The  chief  criticism  to  be  raised  in  regard  to  American  min- 
ing and  tunnel  practice  has  been  that  until  recently  the  economy 
gained  by  using  the  highest  known  explosives  for  such  work  in 
hard  ground  has  not  been  realized. 

TABLE  I.    SHOWING  SPEED   ATTAINED   IN  TUNNEL  DRIVING  IN  AMERICA 


Name  of  Tunnel 

Size  of 
Heading 

Description  Rock 

Highest 
Footage 
per  Month 

Average 
over  Six 
Months 
or  More 

Elizabeth  Lake  
Gunnison  
Gunnison 

12  X  12  ft. 

8  X  12  ft. 
8  X  12  ft. 

Granite 
Soft  shale 
Granite 

466  &  476 

842 
449 

625 

Ophelia  

9  X    9  ft. 

Granite,  basalt,  phonolite 

395 

Newhouse  

6  X    9  ft. 

Granite,  gneiss 

290 

Les  Angelos  Aqueduct 
Kellogg 

101  X  81ft. 
8  X    6  ft. 

Soft  sandstone 
Hard  rocks 

1061 
354 

Roosevelt 

6  X  10  ft. 

Hard  granite 

435 

Hot-Time  Lateral.  .  . 

5  X  7Ht. 

Hard  granite 

263 

238 

292 


ROCK   DRILLS 


TABLE  II.     SHOWING  SPEED  ATTAINED  IN  TUNNEL  HEADING  DRIVING 

IN  EUROPE. 


Name  of  Tunnel 

Size  of  Heading 

Description  of  Rock 

Highest 
Footage  per 
Month 

Average  over 
Six  Months 
or  More 

Simplon  
Arlberg 

6i  X  9^  ft. 
about  same  siz( 

Gneiss  and  schist 
Schist 

755 

641 

426  ft. 
400  ft 

Albula  

a         ft        « 

Gneiss 

607 

550  ft. 

Loetschberg.  . 

«            a           it 

j  Soft  rock 
(  Hard  schist 

1013 
574 

342  ft. 

St.  Gothard  .  . 

n           (i           « 

Gneiss 

563 

Karawanker.  . 

ii           tt          <i 

Schist 

553 

WOLVERINE  MINE,  LAKE  SUPERIOR,  MICHIGAN  * 

Rand  drills  are  used,  the  standard  size  being  3  in.;  they  are, 
however,  turned,  as  worn,  to  3yV,  3|,  and  3y\  in.,  with  pistons  to  fit. 
They  are  mounted  on  both  columns  and  tripods,  usually  the  former, 
although  tripods  are,  in  rare  instances,  employed  in  large  stopes, 
where  the  work  of  drilling  has  more  the  nature  of  quarrying. 

There  is  comparatively  little  drifting  done  in  the  copper 
mines,  except  when  cross-cuts  a  redriven  connecting  different 
lodes,  and  occasionally  on  the  levels  where  barren  rock  is  encoun- 
tered. Some  details  of  drilling  in  drifts,  showing  considerable 
variations,  are  given  in  Table  I. 

TABLE    I 


Number  of 
Hole 

Total  Time  of 
Drilling  per 
Hole 

Delays 

Actual  Time 
of  Drilling 
per  Hole 

Depth  of 
Hole 

Remarks 

Number  of 
Bits  Used 
per  Hole 

1 

31  min. 

5  min. 

26  min. 

5|  ft. 

Wet 

4 

2 

32  min. 

5  min. 

27  min. 

5$  ft. 

Wet 

4 

3 

37  min. 

7  min. 

30  min. 

sift. 

Dry 

4 

4 

38  min. 

7  min. 

31  min. 

5£ft. 

Dry 

4 

5 

148  min. 

48  min. 

100  min. 

5    ft. 

Dry 

3 

6 

50  min. 

10  min. 

40  min. 

6    ft. 

Dry 

4 

Drift  stoping  consists  in  carrying  both  a  drift  and  a  portion 
of  a  stope  together,  the  total  width  being  25  ft.;  6  ft.  of  which 
are  considered  as  drift,  the  remaining  19  ft.  as  stope.  Occasion- 
ally stoping  is  begun  after  a  drift  has  been  run,  which  operation 
is  then  cutting-out  stoping.  Data  taken  from  observations  on 
three  holes  in  drift  stoping  are  given  in  Table  II,  page  293. 
1  By  W.  R.  Crane,  Eng.  and  Min.  Journ.,  Sept.  8,  Oct.  6  and  20,  1906. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 
TABLE  II 


293 


Operation 

l 

2 

3 

Size  of 
Bits 

Setting  drill                   .          

3'  45" 

21'  00" 

5'  50" 

2iin. 

Drilling                                .  .          

9'  45" 

8'  20" 

21'  10" 

2|in. 

Changing  bit                                           •  • 

34'  00" 

55'  00" 

4'  00" 

2|in. 

Drilling                            

8'  26" 

4'  25" 

12'  00" 

2iin. 

Changing  bit                           

0'48" 

I'OO" 

1'15" 

2  in. 

Drilling                                  .              .... 

7'  11" 

7'  55" 

I'OO" 

2  in. 

Changing  bit 

0'59" 

0'40" 

3'  00" 

1!  in. 

Drilling                            

8'  27" 

15'  30" 

9'  45" 

1|  in. 

Changing  bit                                   

2'  43" 

4'  30" 

If  in. 

Drilling 

8'  7" 

6'  00" 



If  in. 

Delay                          

0'45" 



If  in. 

Drilling                                          



7'  35" 



If  in. 

Total  time 

84'  15" 

132'  40" 

58'  00" 

Actual  time  . 

41'  56" 

48'  5" 

43'  55" 



Delays                                              

39'  15" 

82'  55" 

14'  5" 



Depth  of  hole 

9  ft. 

9Ht. 

5£  ft. 

Kind  of  hole    

Wet 

Wet 

Dry 

— 

Cutting-out  stopes  may  begin  at  a  drift,  as  mentioned  above, 
but  as  a  usual  thing  the  term  is  applied  to  the  work  of  stoping 
by  cutting  off  portions,  of  more  or  less  definite  thickness,  succes- 
sively from  the  face  of  a  stope,  beginning  with  and  proceeding 
upward  from  a  drift  or  drift-stope  face.  It  may  be  considered 
as  stoping  proper,  as  it  comprises  the  greater  part  of  the  stoping 
operations  by  which  the  ore  is  removed  from  the  vein  between 
levels,  with  the  exception  of  pillars  left  for  support  of  the  hanging 
wall.  Rates  of  drilling  for  stoping  are  given  in  Table  III. 


TABLE  III 


Number  of  Hole 

Time  Required  to  Drill 
1  ft.  of  Hole 

Depth  of  Hole 

Number  of  Bits  Used 
per  Hole 

1 

4.33  min. 

6ft. 

4 

2 

7.2    min. 

6ft. 

4 

3 

2.7    min. 

10ft. 

5 

4 

8.0    min. 

6ft. 

4 

5 

8.23  min. 

5ft. 

3 

6 

7.60  min. 

7ft. 

4 

294 


ROCK  DRILLS 


Raise  Sloping.  —  Raise  stoping  consists  in  driving  from  15  to 
20  ft.  width  of  stope  directly  up  the  pitch  of  the  vein  to  the 
level  above.  Raise  stopes  are  driven  at  the  boundaries  of 
properties,  also  to  form  connecting  passages  between  levels,  for 
air  and  manways,  and  to  form  pillars.  In  certain  mines  they 
are  regularly  driven  300  ft.  apart,  thus  forming  the  so-called 
dead-ends,  or  long  rectangular  pillars,  running  transversely  with 
the  stopes.  Data  regarding  raise  stoping  are  given  in  Table  IV. 

TABLE  IV 


Number  of 
Hole 

Total  Time 
of  Drilling 

Delays 

Actual  Time 
of  Drilling 

Depth  of 
Hole 

Remarks 

Number  of 
Bits  Used 
per  Hole 

1 

46  min. 

8  min. 

38  min. 

7*ft. 

Dry 

4 

2 

54  min. 

9  min. 

45  min. 

7fft. 

Dry 

4 

3 

64  min. 

7  min. 

57  min. 

6|  ft. 

Wet 

4 

4 

115  min. 

28  min. 

87  min. 

7    ft. 

Wet 

4 

5 

45  min. 

8  min. 

38  min. 

8  min. 

Wet 

5 

For  operation  of  raise  stoping,  see  Figs.  175  and  176.  An 
arrangement  of  drill  holes  for  drift  stoping  is  shown  in  Fig.  173, 
while  the  data  regarding  depth  of  holes,  time  of  drilling,  and 
total  depth  of  holes  are  given  in  Table  IV. 

The  arrangement  of  holes  given  is  common;  condition  of 
face  determines  whether  the  work  shall  begin  at  one  side  or  in 
the  middle  —  if  in  the  middle,  drilling  will  be  carried  on,  on 
both  sides;  i.e.,  the  holes  will  slope  upward  toward  the  middle 
from  the  sides,  instead  of  sloping  all  one  way,  as  when  the  work 
begins  on  one  side.  Raise  stoping  is  paid  for  by  the  fathom,  sim- 
ilar to  the  stoping  part  of  drift  stoping.  The  amount  broken 
down  in  the  stope,  shown  in  the  Fig.  176,  is  4  fathoms  (5|  ft. 
deep  by  20  ft.  long  by  8  ft.  high,  divided  by  216  ft.).  Delays 
other  than  those  common  to  drilling  and  setting  up  will  reduce 
this  one  half  or  to  about  2  fathoms  for  2  shifts.  As  there  are 
2  shifts  per  day  and  26  days  per  month,  52  fathoms  per  month 
would  be  broken  down,  which  at  an  expense  of  $4.24  gives  $220.48 
to  be  deducted  from  $416,  which  is  the  amount  received,  leaving 
$195.52  profit  for  the  month.  Cutting-out  stoping,  or  stoping 
proper,  consists  in  removing  the  vein  content  in  a  more  or  less 
regular  way;  i.e.,  by  cutting  out  a  portion  of  definite  width  from 


EXAMPLES  OF  ROCK  DRILL  PRACTICE  295 

the  face  of  the  drift  or  drift  stope  and  parallel  with  it.  Stoping 
under  these  conditions  is  most  favorable  to  rapid  work  in  drilling 
and  clearing  away  the  broken  rock,  as  the  work  is  done  on  a  broad 
face.  The  price  paid  per  fathom  is  the  same  as  with  other  stoping 
operations.  When,  however,  the  ground  breaks  readily  and  the 
stopes  are  large,  the  amount  paid  is  reduced  even  as  low  as  $5.50, 
while  under  less  favorable  conditions  a  higher  price  may  be  paid. 
Where  the  levels  have  to  be  extended  entirely  in  ore  and 
wide  openings  can  be  made  without  timbering  and  no  pillars  are 
required  along  the  back  of  the  level,  the  system  of  stope  drives 
adopted  allows  of  great  economy  in  the  placing  of  holes  and 
the  use  of  explosive.  The  great  length  of  face  exposed  allows 
" eating  in"  holes  to  be  arranged  as  shown,  and  fired  with  the  mini- 
mum of  explosives  per  ton  of  ore  broken.  The  stope  raise  is 
economical  for  the  above  reason  also. 

STOPING  AND  DRIFTING  AT  LAKE  SUPERIOR  l 

The  comparatively  hard  and  rather  solid  amygdaloid  forma- 
tion of  the  Kearsarge  lode,  northern  Michigan,  makes  the  drilling 
operations  somewhat  difficult,  although  the  prevailing  low  pitch 
of  the  lode  renders  the  setting  up  of  the  drill  easy.  The  mining 
operations,  including  development  work,  may  be  considered  in 
the  following  order :  Shaft  sinking,  drifting,  and  stoping.  Stoping 
may,  for  convenience,  be  subdivided  into  drift,  cutting  out,  and 
raise  stoping. 

Drifting.  —  Drifts  are.  usually  driven  6  ft.  wide  and  7  ft. 
high,  although  practice  varies  considerably  with  respect  to  size. 
An  arrangement  of  holes  employed  in  drifting  in  the  Mohawk  and 
Wolverine  mines  is  shown  in  Fig.  172.  The  lower  portion  of  the 
face  is  first  removed  by  a  number  of  short  downward  pitching  holes, 
as  shown,  although  an  initial  opening  or  sump  may  be  formed 
by  grouping  a  number  of  holes  in  one,  usually  the  right-hand 
lower  corner.  Having  thus  unbound  the  lower  part  of  the  face,  the 
remaining  portion  is  broken  out,  following  which  the  upper  portion 
is  knocked  down  by  shots  placed  in  holes  drilled  as  shown  in  Fig.  172. 

The  depths  of  the  individual  holes  for  drifting  are  given  in 

Table  I,  while  in  the  last  two  columns  are  the  total  depth  of  the 

hole  for  a  complete  round,  and  the  time  required  in  drilling  them. 

The  time  is  calculated  by  multiplying  the  total  depth  of  the  holes, 

1  W.  R.  Crane,  Eng.  and  Min.  Journ.,  Oct.  6,  1906. 


296 


ROCK  DRILLS 


Total  Time 

d 
'§  J 

CO  ^ 

I—  '      r^M 

.  T8 

^- 

CO 

i—  i 

d 

'S  <* 

10   45 

^  ^ 

2  ^ 

^    (N 

t-H 

<N 

d 
S  3 
^3 

^      M 
^    <N 

GO 

T—( 

Total  Depth 
in  Feet 

»o 

GO 

oo 

0 

•* 
t^ 

rH 

0 
1—  1 
"tfl 

1 

d 

3 

0 

jj 

"a 

V 

Q 

S 

iO 

M 

55 

10 

JH 
(N 

iO 

id 

§5 

iO 

no 

R 

*> 
t*- 

(N 

p 
»d 

O 
00 

iO 
cd 

S 

»o 
id 

p 

GO 

>o 

CO 

O5 

iO 

id 

0 
OS 

0 
t^ 

00 

o 
id 

o 

OS 

O 

1> 

^s. 

iq 
id 

0 
OS 

»o 
t^ 

0  1      « 

^     1          10 

iO 
cd 

o 

CO 

iO 

»o 
id 

iO 

cd 

O 
l^ 

•<* 

iO 

»d 

>o 
** 

O 

GO 

ec 

p 

CO 

lO 

•^ 

O 
I> 

C<l 

o 
^ 

o 

GO 

iO 
CO 

S 

p 

id 

o 

GO 

iO 
cd 

o 

LO 

id 

0 
00 

»O 

CO 

O> 

0 
rj5 

p 

(N 

0 
•<*i 

00 

O 
(N 

« 

O 
•^ 

t^ 

0 
CO 

»o 

iO 

0 

Tj5 

to 

IO 

CO 

o 

GO 

iO 
GO 

1C 

o 

(N 

o 

GO 

O           I 
OS 

••*! 

o 

Tj5 

o 

GO 

to 

GO 

eo 

iO 
CO 

iO 
GO 

IO 
CO 

(N 

o 

CO 

iO 
GO 

O 
GO 

- 

0 

CO 

iO 

GO 

iO 
cd 

No.  of  Holes 

b/D 

.  a 
Q 

Drift  sloping 

bC 

d 

•a 
1 

o 

02 

1 

H!§! 


15* 


CO   CO   <N   i-H 

T^  id  id  cd 


^        t^-     OS     i-H 

I-H    (N    CO   O 

OS    t-^    CO    GO 


8^S^ 

CO    OS    00    ^-H 


S:  fc  fc  S: 

TfH  O  »0  O 

cb  ^  OS  ^H 

CO  (N  CO  IO 


fe          fc          S: 

CO 
<M 


^^ 


CO   ^C   no 
iO   I>    CO 


, 

"S  °  o 

**1 


^     «     bfi 


S  .S 


v 


-c  s 
Q  O 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


297 


in  feet,  of  a  complete  round,  by  the  time  required  to  drill  one 
foot  of  hole.  (See  Column  6,  Table  II.)  The  time  thus  obtained 
is  13  hours,  16  min.,  which,  as  the  length  of  a  shift  is  10  hours, 
gives  approximately  1J  shifts. 

The  advance  made  on  shooting  the  round  of  holes  is,  as  shown 
in  Fig.  172,  more  than  4  ft.,  or  about  two  thirds  of  the  longest 
hole,  probably  a  fair  estimate.  The  advance  made  per  month 
on  a  basis  of  4  ft.  per  1J  shift  would  be  69.2  ft.  The  practice  is 
not,  however,  to  fill  a  complete  round  of  holes  before  charging 
and  firing,  but  rather  to  fill  a  few,  charge  and  fire,  then  clean  up, 


*  . 

j*  ----    6    ----  »| 


FIG.  172.  —  Arrangement  of  holes  in  drifting  as 
practised  in  Lake  Superior  district. 

and  so  on  until  the  advance  has  been  made.  .It  is  then  evident 
that  much  time  is  spent  other  than  in  drilling.  The  usual  time 
taken  for  an  advance  is  2|  to  3  shifts,  and  as  only  1  shift  is  worked 
a  day,  from  2J  to  3  days  are  required  for  an  advance  of  4  ft.  In 
26  working  days  (one  month)  there  would  then  be  10.4  advances 
made,  which,  at  4  ft.  to  the  advance,  gives  41.6  ft.  The  rates  of 
advance  for  a  number  of  months'  work  in  the  drift  in  question 
range  from  30  to  43  ft.,  averaging  40  ft. 

Drifting  is  paid  for  at  the  rate  of  $8  to  $8.50  per  linear  foot. 
The  cost  of  drifting  itemized  is  as  follows :  Eight  boxes  of  powder, 
$136;  one  box  of  candles,  $8;  1100  ft.  fuse,  $11;  three  boxes  caps, 
$6;  three  gallons  of  oil,  90c.;  drill  boy,  $15;  steel,  $2.  Total, 


298 


ROCK  DRILLS 


of 


$178.90.     An  advance  of  40  ft.  at  $8  gives  $320,  which,  minus 

expenses,  leaves  $141.10,  or    $70.55 
per  man  per  month. 

Sloping.  —  Drift  stoping  is  the 
usual  method  of  developing  and  work- 
ing a  level,  and  consists  in  carrying 
a  face  25  ft.  wide  practically  the  full 
hight  of  the  lode  —  the  lower  part 
includes  the  drift,  and  is  run  at  the 
required  grade  of  the  level.  A  com- 
mon arrangement  of  holes  for  drift 
stoping  is  given  in  Fig.  173,  although 
no  exact  rule  can  be  given  regarding 
the  practice;  conditions  and  character 
of  rock  govern.  When  possible,  how- 
ever, the  lower  or  drift  portion  is  at- 
tacked first,  thus  forming  a  sump  into 
which  the  remaining  upper  portion  is 
broken.  Length  of  holes,  total  depth 
of  holes,  and  time  of  drilling  are 
given  in  Table  I,  page  296. 
Stoping  is  paid  for  by  the  fathom, 
the  exact  amount  varying  with  the 
particular  stope  and  conditions  pre- 
vailing therein;  $6  to  $9  per  fathom 
is  common,  average  probably  $8.  A 
fathom  is  216  cu.  ft.  (6  X  6  X  6). 
The  average  hight  of  stope  is  12 
ft.,  or  2  fathoms,  the  miner  being 
paid  for  that  hight  of  stope,  regard- 
less of  whether  the  actual  hight 
exceeds  or  falls  below  it.  In  drift 
stoping  the  width  of  drift  is  sub- 
tracted from  the  width  of  stope, 
that  portion  being  paid  for  as  drift- 
ing rather  than  stoping;  $5.50  is  the 
usual  rate  per  foot.  The  miner  then 
receives  $8  a  fathom  for  19  ft.  width 
of  stope,  12  ft.  high,  and  $5.50  per 
foot  of  drift,  6  ft.  wide  by  12  ft.  high. 


Fia.    173.  —  Arrangement 
holes  in  drift  stoping. 


FIG.    175.  —  Arrangement 
holes  in  raise  stoping. 


EXAMPLES  OF   ROCK   DRILL  PRACTICE  299 

The  amount  of  rock  mined  in  the  stope  shown  in  Fig.  173  is 
about  4J  fathoms,  steady  drilling  for  two  shifts;  but  owing  to 
cleaning  up  and  delays  other  than  those  attendant  upon  drilling, 
which  have  been  considered,  not  more  than  one  half  of  this  amount 
can  be  broken  down  regularly,  and  2J  fathoms  may  be  considered 
a  fair  estimate.  As  there  are  two  regular  shifts  per  day,  the  num- 
ber of  fathoms  per  month  would  be  58|,  which,  at  $8,  gives  $468 
per  month.  Two  drilling  crews  must  divide  this  amount  among 
themselves,  each  man  receiving  $117,  from  which  the  expenses 


FIG.  176.  —  Raise  stoping.    Breaking  through. 

must  be  deducted.  A  drill  boy  serves  two  crews,  his  wages 
being  divided  equally  between  them.  In  a  similar  manner  the 
company  charge  of  $4  for  drill  steel  per  drill  per  month  is  divided 
between  the  crews. 

Details  of  miners'  expenses  in  stoping  are  as  follows:  Candles, 
2  boxes,  $16;  powder,  7  boxes,  $119;  fuse,  800  ft.,  $8;  caps,  200, 
$4;  oil,  3  gal.,  90  cents;  drill  boy,  $15;  steel,  $2.  Total,  $164.90. 
Incident  with  this  expense,  40  fathoms  were  broken  down,  which 
at  $8  gives  $320.  Deducting  expenses,  there  remains  $155.10. 


300  ROCK  DRILLS 

The  expense  per  fathom,  average  of  a  number  of  accounts, 
is  $4.24.  The  cost  of  the  58J  fathoms  is  then  $248,  which, 
deducted  from  the  amount  received,  $468,  leaves  $220  profit 
for  the  19  ft.  of  stoping.  The  expense  of  driving  the  drift  por- 
tion of  the  stope  a  distance  corresponding  to  the  advance  of  the 
stope  portion,  6J  ft.,  at  $4.44  per  ft.,  amounts  to  $28.86,  while 
there  was  received  for  that  advance  $35.75.  The  total  expense 
and  amount  received  for  advancing  the  drift  stope  6J  ft.  are 


FIG.  177.  —  Longitudinal  section  of  shaft,  Wolverine  mine. 

$276.86  and  $503.75,  leaving  a  profit  of  $226.89,  which,  divided 
among  four  men,  gives  $56.72  per  month. 

SHAFT  SINKING  AT  THE  WOLVERINE  MINE/  MICHIGAN 

Shaft  sinking  is  carried  on  slowly  and  the  arrangement  shown 
by  Dr.  Crane  is  the  one  found  most  suited  to  the  circumstances. 

"The  work  preliminary  to  shaft  sinking  consists  in  preparing 
the  last  station,  at  the  foot  of  the  shaft  to  be  extended  by  flooring 
up  to  the  level  of  the  drift.  A  small  sinking  shaft,  often  the  size 
1  W.  R.  Crane,  Eng.  and  Min.  Journ.,  Oct.  20,  1906. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


301 


of  only  5-|  X  5J  ft.,  but  usually  5J  ft.  wide  by  9  ft.  long,  is  begun 
in  line  with  the  manway  portion  of  the  finished  shaft  above.  It 
is  usually  driven  for  a  distance  of  6  to  7  ft.,  after  which  it  is 
abruptly  enlarged  to  the  full  size  of  the  main 
hoisting  shaft  and  in  exact  alignment  with  it. 
The  enlargement  must  then  of  necessity  be  all 
on  one  side,  which  is  to  the  right  of  that  of 
the  initial  opening.  A  block  of  undisturbed 
rock  is  thus  left  directly  below  the  hoisting 
compartment  of  the  shaft  above,  insuring  ab- 
solute  safety  to  the  operations  conducted 
below.  The  block  of  unmined  ground  is  called 
a  pentice,  and  is  shown  in  Figs.  177  and  178. 
"The  sinking  of  the  shaft,  after  the  full 
section  has  been  attained  by  the  enlargement 


PLAN  OF  FACE. 


LON&  SECTION 


ROCK 

of  the  small  opening  to  the  pentice,  is  accom-  FIG.  178.  —  Arrange- 
plished  by  one  drilling  crew,  as  stated  above,  ment  of  holes  m 
and  there  is,  therefore,  but  one  drill  employed,  ^^  ££*"*• 
which  is  mounted  upon  a  column.  The  holes 

are  usually  placed  as  shown  in  Fig.  179,  i.e., 
they  are  arranged  to  take  advantage  of  the 
shape  and  condition  of  the  working  face.  A 
depression  or  re-entrant  angle  in  the  face  indi- 
cates the  point  of  attack;  if  at  one  end  of  the 
shaft  section  the  holes  are  drilled  as  shown, 
but  if  at  or  near  the  middle  the  holes  are 
drilled  on  both  ends  of  the  section,  and  slope 
toward  the  middle.  The  arrangement  of  holes 
is  practically  the  center  or  draw-cut  system, 
which  is  modified  largely  by  character  of  rock 
and  local  conditions." 


•  »••-.•—  .»::v 

*---.•    - 

•  °.  »-..»--.*r.-»- 

'-.v-     ~ 

FIG.  179.  —  Arrange- 
ment of  holes  in 
shaft  sinking,  Wol- 
verine mine. 


ROCK-DRILLING  PRACTICE  AT  JOPLIN, 
MISSOURI 


We  have  here  an  example  of  working  in 
ore  that  drills  and  breaks  easily.  Large  faces  are  available  and 
often  free  on  three  sides;  hence  long  holes  are  drilled  to  advan- 
tage. They  are  first  enlarged  to  hold  large  charges  of  low-grade 
powder.  As  in  Lake  Superior  region,  drifting  and  stoping  are 
combined  to  give  large  faces  of  attack. 


302  ROCK   DRILLS 

The  following  description  of  the  methods  of  breaking  ore  in 
sheet  ground  l  at  Joplin,  Missouri,  is  given  by  Doss  Brittain. 

" Raid  Ground  Sloping.  —  Hard  ground  consists  of  massively 
bedded  rock  requiring  heavy  blasting  to  loosen  it.  Such  ground 
is  to  be  found  throughout  the  district  in  the  same  localities  as 
the  soft  ground,  but  more  extensively. 

"All  hard  ground  breaking  is  done  with  machine  drills  and 
powder.  The  type  of  drill  in  most  common  use  is  the  Sullivan 
U  C,  and  the  Ingersoll  C  24  for  shaft  sinking,  and  the  Sullivan 
U  F  2,  and  the  Ingersoll  C  24  for  heavy  stoping.  A  few  lighter 
and  a  few  heavier  drills  of  the  same  make  are  in  use,  but  are  not 
common.  Nearly  all  of  the  machine  drills  in  use  are  air  drills, 
though  some  steam  drills  find  employment  in  the  district.  Hand 
steel  cannot  be  said  to  find  a  use  there  in  breaking  hard  ground; 
it  was  discarded  when  deeper  mining  began.  In  ordinary  ground 
an  average  8-hour  shift's  work,  for  a  drill,  is  45  ft.  of  holes.  Steels 
have  to  be  changed  with  a  frequency  varying  with  the  hardness 
of  the  ground  and  the  skill  used  in  tempering.  In  most  cases  a 
change  is  required  every  two  or  three  feet,  while  in  others  a  bit 
can  be  used  for  twice  this  distance.  The  bit  employed  most 
commonly  is  known  as  the  bull-head  or  chisel  bit,  with  the  cut- 
ting edge  in  a  straight  line.  Some  of  the  larger  Webb  City  mines, 
however,  employ  the  diamond-edge  bit  with  cutting  edge  arranged 
in  the  form  of  a  cross.  In  shaft  sinking  the  holes  are  usually 
started  with  If-in.  steel  and  finished  with  the  1-in.  size.  In 
stoping  the  holes  are  usually  started  with  IJ-in.  steel  and  finished 
with  the  If-in.  size.  If  the  holes  are  deeper  than  10  ft.  they  are 
usually  finished  with  smaller  steel. 

"In  order  to  break  the  greatest  amount  of  ground  at  the  least 
cost,  it  has  been  found  advisable  in  most  cases  to  'squib/  'bull,' 
or  'spring'  the  holes  before  putting  in  and  firing  the  charge 
intended  to  accomplish  the  work  of  real  ground-breaking.  Squib- 
bing  is  the  process  of  enlarging  the  drill  holes  with  powder  so 
that  they  will  hold  more  powder  than  otherwise,  thus  enabling 
each  blast  to  lift  more  ground  than  if  the  holes  were  charged 
without  being  enlarged.  It  is  done  with  from  one  half  to  one 
stick  of  dynamite,  and  is  repeated  sometimes  as  many  as  three 
times  in  very  hard  ground.  Two  or  three  slight  explosions  so 
enlarge  the  hole  that  it  will  hold  from  50  to  75  sticks  of  powder. 
1  Eng.  and  Min.  Journ.,  Dec.  14,  1907. 


EXAMPLES  OF   ROCK   DRILL   PRACTICE  303 

The  hole  is  then  cleaned  with  a  blow-pipe  made  for  the  purpose, 
and  charged  with  the  heavy  charge. 

"  In  charging,  the  sticks  are  usually  split  down  the  side  so  that 
when  tamped  they  will  spread  readily.  Each  stick  is  placed  on 
the  sharp  end  of  a  spoon  and  pressed  to  the  bottom  of  the  hole, 
where  it  is  tamped  with,  a  round  wooden  tamping  stick  of  oak 
or  hickory  8  to  12  ft.  long.  The  last  stick  or  part  of  stick  passed 
in  contains  the  cap,  or  primer,  and  fuse,  electric  firing  being 
employed  in  the  district  only  for  sinking  purposes.  This  last 
stick  is  called  the  starter  and  is  prepared  by  making  a  round 
cavity  in  the  end  of  the  mass  of  powder  with  a  sharp  stick.  The 
primer  is  slipped  over  the  end  of  the  fuse  and  tightly  crimped 
with  a  pair  of  pincers  or  the  teeth  so  as  to  prevent  water  from 
moistening  the  primer.  The  end  of  the  fuse  bearing  the  primer 
is  then  inserted  into  the  hole  in  the  starter  and  the  paper  covering 
is  drawn  up  over  the  fuse  above  the  primer  and  securely  tied 
with  a  stout  string.  As  additional  precaution  against  moisture 
in  very  wet  mines  the  tar  melted  from  a  piece  of  fuse  is  allowed 
to  drop  around  the  junction  of  the  cap  and  fuse  before  intro- 
duction into  the  starter.  The  latter,  after  being  prepared  to  suit 
local  conditions,  is  inserted  into  the  drill  hole  in  intimate  con- 
tact with  the  charge.  The  hole  is  then  tamped  full  of  clay  and 
gravel  to  prevent  ths  charge  from  being  wasted  by  blowing  out 
through  the  hole,  and  the  blast  is  ready  for  firing,  which  is  the 
only  thing  now  necessary  to  complete  the  utility  of  the  drill  and 
dynamite.  About  1  Ib.  of  dynamite  is  required  for  every  ton  of 
ground  broken  in  drifting,  and  25  Ib.  to  the  foot  for  sinking 
shafts  of  ordinary  size. 

"  Shaft  Sinking.  —  As  a  rule  12  holes  are  drilled  in  the  bottom 
of  the  shaft  and  are  arranged  as  indicated  in  Fig.  180.  The  four 
holes  occupying  the  middle  of  the  shaft,  and  known  as  sump 
holes,  are  inclined,  or  "look,"  inward  toward  the  center  of  the 
shaft  at  an  angle  of  about  30°  from  the  vertical.  They  have 
a  slant  hight  of  about  5  ft.  and  pull  vertically  about  4  ft. 
Four  other  holes  are  driven  about  1  ft.  from  the  corners  respec- 
tively and  look  slightly  outward,  so  that  the  shaft  will  break  to  a 
uniform  width  as  it  progresses  downward.  Likewise  the  four 
holes  near  the  middle  of  the  sides  look  outward  for  the  same 
purpose.  Both  the  corner  holes  and  those  at  the  sides  are  sunk 
about  4  ft.,  so  that  they  will  pull  vertically  the  same  distance  as 


304 


ROCK  DRILLS 


the  sump  holes,  which  are  fired  first.  These  are  followed  by 
the  side  holes  and  these  by  the  corner  holes.  The  reason  for  the 
order  is  evident  when  the  area  blasted  out  by  each  series  of  shots, 
as  indicated  in  Fig.  180,  is  considered.  Figs.  181  and  182  indicate 


PLAN  OF  SHAFT 


o"' 


s 


o  —  > 


..---I 


FIG.  180.  —  Showing  arrangement  of  holes  in  shaft  sinking  at  Joplin. 

other  arrangements  of  holes  for  shaft  sinking  which  are  now  rarely 
used  except  for  shale  or  other  soft  formations. 

11  Drifting.  —  In  the  arrangement  of  holes,  Fig.  183,  the  same 
principles  obtain  as  to  depth,  inclination,  and  indicated  order  of 
firing  as  in  the  case  of  shaft  sinking. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE 


305 


\ 

' 


PLAN  OF  SHAFT 


SECTION  OF  SHAFT 

FIG.  181.  —  Showing  arrangement  of  holes  in  shaft  sinking,  Joplin. 


V 


PLAN  OF  SHAFT 


SECTION  OF  SHAFT 

FIG.  182.  —  Showing  arrangement  of  holes  in  shaft  sinking,  Joplin. 


306 


ROCK  DRILLS 


''When  the  ore  is  reached,  or  if  the  drift  started  in  ore,  when  it 
reaches  a  distance  sufficient  to  keep  the  shaft  from  caving,  it  is 
widened  to  about  50  ft.,  or  until  the  width  of  the  ore  deposit 
is  embraced.  This  widened  excavation,  the  heading  of  which  is 
usually  8  ft.  high,  the  hight  of  the  drift,  of  which  it  is  but  a  wide 
expansion,  proceeds  along  the  top  of  the  orebody.  If  this  be  more 
than  the  hight  of  the  heading  in  thickness,  a  step,  or  stope,  is  taken 
up.  Should  there  still  be  ore  in  the  drift,  more  stopes  are  taken 
up  until  the  orebody  is  exhausted.  Regularly  two  stopes  are 
carried  at  once,  giving  -the  wide  drift  a  depth  of  30  ft.,  including 


lO— > 

il 


\ 

•         \ 

ox' 


FIG.  183.  —  Arrangement  of  drift  holes,  Joplin,  Mo. 

8  ft.  for  the  heading  and  11  ft.  for  each  stope,  which  begins  at 
the  shaft,  thus  keeping  the  floor  of  the  narrow  drift  always  on  a 
level  with  that  of  the  wider  drift  so  as  to  furnish  a  comparatively 
level  surface  for  hauling  the  ore  to  the  shaft.  The  heading  and 
stopes  are  kept  about  10  ft.  ahead  of  the  stope  below.  For 
carrying  such  a  drift  the  holes  for  blasting  are  arranged  as 
indicated  in  Fig.  184. 

"The  first  four  holes  at  either  end  of  the  heading  are  drilled 
5  ft  deep,  the  other  7  ft.  The  next  series  of  heading  holes,  after 
the  first  is  fired,  is  arranged  with  the  shallow  holes  at  the  reverse 
end  of  the  heading,  so  that  each  series  of  shots  breaks  the  face 


EXAMPLES   OF  ROCK   DRILL   PRACTICE 


307 


of  the  heading  at  a  right  angle  with  the  direction  of  the  drift, 
thus  releasing  or  unbinding  the  rock  to  be  blasted.  The  shallow 
holes  are  fired  first,  for  the  obvious  purpose  of  making  the 
deeper  shots  more  effective.  The  holes  drilled  in  the  first  stope 
are  arranged,  as  also  indicated  in  Fig.  184,  in  two  rows  of  three 
holes  each,  one  at  each  corner,  and  one  near  the  middle  of  the 
top  and  the  bottom  of  the  stope. 

"  Orebody.  —  The  average  thickness  of  ore  is  6  to  9  ft.,  though 
it  is  sometimes  followed  as  thin  as  2  ft.,  and  has  occurred  25  ft. 


/" 

0000 

J 

1 

1              '4              2              2 

0 

0                     0                     O                     0 

I 

1 

1               2               2               2 

f 

O 

3 

0                                                0 

1                                2 

J 

• 

o 

0                                             0 

4-                              6 

: 

e.  

80-ft-r  ,  » 

o 
>  —  3—  - 

?                        2 

Faces  of  Stopes 


Section  through  Stopes.  and  Profile 


Section  through  A-A 

FIG.  184.  —  Drift  stoping,  Joplin,  Mo. 

thick.  Two  layers  of  mineral  separated  by  a  thin  layer  of  rock  are 
removed  simultaneously  with  the  dividing  seam.  Mineral  rarely 
occurs  here  in  layers  so  far  apart  as  to  prohibit  working  in  this 
manner.  When  widely  separated  they  are  sometimes  worked 
simultaneously,  but  more  often  the  upper  stratum  is  exhausted 
before  the  lower  is  touched,  except  for  developing  purposes. 

'  Breaking  the  Ore.  —  The  mineralized  ground  is  composed  of 
very  hard  flint,  compactly  bedded.  A  wide  range  of  notions 
prevails  as  to  methods  of  ground-breaking,  but  the  conventional 
position  of  the  holes  and  their  number  are  represented  in  Fig.  185. 
Each  set  of  four  holes,  considered  a  round,  should  break  an  aver- 


308 


ROCK  DRILLS 


age  of  30  tons  of  dirt,  9  to  10  ft.  laterally  and  from  the  roof  to 
the  floor.  The  top  hole,  No.  2,  on  the  vertical  median  line  of 
the  area  to  be  broken  and  very  near  the  roof,  is  so  directed  as 
to  break  the  roof  level.  Holes  No.  1  and  No.  3,  equidistant 
from  the  median  line,  are  3  ft.  from  each  other  and  the  roof. 
The  stope  hole,  No.  4,  as  near  the  floor  as  the  drill  will  allow, 
slants  so  the  shot  will  lift  clean  to  the  floor.  The  lateral  direc- 
tion of  these  holes  varies  with  the  individual  taste  of  the  machine 
man.  All  are  uniformly  9  ft.  deep,  started  with  a  IJ-m-  bit,  and 
finished  with  a  If  to  1-in.  steel. 

"  After  squibbing  to  enlarge  the  bound  end  of  the  hole  for 


FIG.  185.  —  Arrangement  of  holes  for  breaking  ore,  Joplin,  Mo. 

powder,  the  holes  are  loaded  with  50  Ib.  of  powder,  Nos.  1,  2, 
and  3  receiving  half  and  No.  4  the  remainder.  The  blasts  are 
fired  as  numbered  in  the  figure." 

ROCK-DRILLING  PRACTICE  IN  UTAH 

The  following  data  concerning  the  method  of  quarrying  the 
soft  porphyries  of  Bingham,  Utah,1  are  given  by  W.  R.  Ingalls. 

"  Loosening  the  Ground.  —  The  Boston  company  loosens  the 
ground  by  sinking  holes  with  churn  drills  and  exploding  large 
charges  of  dynamite  in  them.  It  has  five  Keystone  drills  for 
this  work.  These  use  a  5|-iri.  bit,  making  a  hole  about  6J  in. 
in  diameter,  which  is  sunk  to  a  depth  of  150  or  160  ft.  The  holes 
are  put  down  15  to  20  ft.  below  the  level  of  the  bench  that  is 
1  Eng.  and  Min.  Journ.,  Sept.  7,  1907. 


EXAMPLES  OF  ROCK  DRILL  PRACTICE  309 

being  broken,  so  as  to  insure  loosening  of  the  ground  below  the 
level  on  which  the  steam  shovel  is  at  work  and  prevent  the  exist- 
ence of  unbroken  knobs  in  the  floor,  which  would  be  troublesome 
to  the  shovel.  The  holes  are  put  down  about  30  ft.  apart  and  at 
such  distance  back  from  the  face  of  the  bench  that  the  horizontal 
distance  from  the  face  at  the  bottom  will  be  about  30  ft.  From 
six  to  nine  holes  are  shot  at  a  time,  with  1200  to  4700  Ib.  of  dyna- 
mite per  hole.  Dynamite  with  40  and  60  per  cent,  of  nitro- 
glycerine is  used,  the  former  grade  being  most  commonly  employed. 
This  grade  costs  11.5  c.  per  Ib.  at  Bingham.  As  much  as  225,000 
tons  of  rock  have  been  dislodged  by  a  blast  of  nine  holes,  the 
powder  cost  being  about  1.5  c.  per  ton. 

"  In  the  Utah  mine  the  ground  is  loosened  by  means  of  3j-in. 
Ingersoll  air  drills,  which  put  down  holes  20  ft.  deep  with  IJ-in. 
steel  star  bits.  These  holes  are  put  down  15  to  20  ft.  apart,  about 
20  ft.  back  from  the  face.  It  is  obviously  a  less  efficient  method 
of  loosening  the  ground  than  that  which  has  been  adopted  by 
the  Boston  company.  The  extensive  character  of  the  under- 
ground workings  in  the  Utah  mine  is  practically  prohibitive  as 
to  the  use  of  churn  drills  there." 

METHOD  OF  EXCAVATING  ROCK  IN  LARGE  MASSES  1 

The  following  notes  are  taken  from  experience  in  heavy  rock 
excavation  on  the  line  of  the  Grand  Trunk  Pacific  Railroad  in 
the  region  of  the  Lake  of  the  Woods.  The  rocks  of  this  locality 
consist  of  hard  granites,  traps,  and  diabase  of  the  Laurentian  and 
Huronian  systems.  Owing  to  the  extreme  hardness  of  the  rocks 
the  expense  of  drilling  is  very  high,  consequently  deep  holes  and 
heavy  blasts  are  used  wherever  permissible. 

"  Hand  and  Machine  Drilling.  —  In  the  smaller  cuts  hand  steel 
is  used  for  putting  down  the  blast  holes,  which  are  often  drilled 
to  a  depth  of  30  ft.;  1-in.  steel  is  used,  and  the  same  gage,  lf-in., 
is  carried  throughout.  The  holes  are  started  with  two  hammers 
on  a  drill,  and  when  down  5  or  6  ft.  the  drill  turner  also  swings 
in  with  a  hammer;  the  rapid  blows  jump  the  steel  enough  to  bore 
a  fairly  round  hole.  The  average  depth  drilled  per  day  by  three 
men  is  16  to  29  ft.,  and  45  c.  is  the  average  price  paid  to  foot 
drillers. 

"  Steam  drills  are  generally  used  in  the  big  cuts,  a  3-in.  machine 
1  By  Geo.  C.  McFarland,  Eng.  and  Min.  Journ.,  Aug.  3,  1907. 


310  ROCK  DRILLS 

drilling  to  25  ft.  and  a  3i  to  3^-in.  machine  drilling  the  depths  of 
30  and  35  ft.  In  using  steam  the  only  change  required  for  an 
air  drill  is  a  steam  front  head  and  thin  paper  gaskets  in  the  outer 
joints.  Flexible  metal  steam  hose  is  used  exclusively,  the  oiler 
being  placed  at  the  end  of  the  steam  pipe  to  lubricate  the  hose 
as  well  as  the  machine.  When  several  drills  are  run  from  the 
same  boiler,  a  sight  feed  lubricator  can  be  placed  on  the  main 
steam  pipe.  This  saves  the  runner  the  bother  of  oiling  and 
insures  a  regular  and  continuous  lubrication  of  the  hose  and 
machines. 

"The  life  of  the  metal  hose  is  about  six  months,  as  against 
two  months  for  the  best  grades  of  rubber  steam  hose.  When 
drilling  over  20  ft.  the  steam  pressure  is  run  up  to  115  Ib.  or  more. 
During  the  past  winter  drills  were  operated  when  the  temper- 
ature was  45°  below  zero,  some  of  the  machines  being  500  to 
600  ft.  from  the  boiler. 

"Drill  Steel.  —  For  deep  holes  the  drill  steels  are  made  up  for 
24-in.  runs,  the  starters  being  gaged  3|  in.  and  the  gage  being 
dropped  f  to  -fg  in.  for  each  succeeding  steel,  so  as  to  finish  the 
hole  about  1J  in.  The  bits  are  forged  with  long,  heavy  shoulders 
and  very  little  clearance  to  reinforce  the  corners  of  the  cutting 
edge  and  prevent  excessive  wear  in  the  gage.  The  last  two  or 
three  drills  of  the  set  are  usually  fitted  with  blunt  chisel  bits. 

"The  cheaper  grades  of  drill  steel  are  used  almost  exclusively; 
the  high-grade  brands  of  bar  and  cruciform  steels  require  to  be 
forged  and  dressed  at  low  heat,  and  even  when  properly  dressed 
and  tempered  wear  as  fast  as  the  low-priced  drills.  The  latter, 
while  they  can  be  forged  at  a  much  softer  heat,  will  not  stand 
excessive  upsetting,  and  it  is  often  good  practice  to  weld  on  short 
lengths  of  heavy  steel  to  form  the  bit. 

"  In  tempering,  the  bit  should  be  toughened  by  heating  to  a 
bright  red  heat,  then  plunged  into  the  water  f  to  J  in.  and  held 
there  15  to  20  seconds,  soused  a  few  times  until  the  part  out  of 
the  water  is  cooled  sufficiently  to  show  no  color,  and  finally 
immersed  in  the  tub  until  cold.  If  tempered  in  this  manner  a 
drill  will  show  \  in.  of  cutting  edge,  with  a  fine  gray  temper  backed 
by  softer  tough  metal. 

"Method  of  Drilling.  —  The  usual  practice  is  to  drill  the  blast 
hole  on  the  center  line  of  the  cut.  A  15-ft.  hole  is  set  back  15  ft. 
and  a  30-ft.  hole  25  ft.  from  the  face  of  the  cut.  Where  the  cut 


EXAMPLES  OF  ROCK  DRILL  PRACTICE  311 

is  much  more  than  30  ft.,  it  is  best  to  take  it  out  in  two  benches. 
In  granite  the  average  footage  drilled  by  a  machine  is  30  ft.  per 
10-hour  shift,  while  in  trap  and  diabase  20  to  25  ft.  is  considered 
a  good  shift's  work. 

"After  drilling,  the  bottom  of  the  whole  is  chambered  to  the 
required  size  by  springing  with  dynamite.  In  the  bottom  bench, 
where  a  heavy  lift  is  required,  no  more  than  a  foot  of  the  hole 
is  chambered;  in  the  upper  benches  it  is  permissible  to  chamber 
2  or  3  ft.  of  the  bottom.  In  the  first  case  each  spring  would  be 
loaded  until  the  dynamite  raised  8  or  10  in. ;  in  the  second,  a  12- 
or  15-in.  raise  would  be  permissible.  The  first  springs  are  held 
down  by  5  or  6  ft.  of  water  tamping  and  detonated  by  a  cap-and- 
drop  fuse.  The  fuse,  usually  12  in.  long,  after  being  split  is  held 
under  water  for  5  or  6  seconds  to  kill  any  fire  hanging  in  the 
taping,  and  then  dropped  into  the  hole.  Unless  the  drop  fuse 
were  dipped  in  water,  it  might  ignite  dynamite  adhering  to  the 
sides  of  the  hole,  causing  a  premature  explosion.  After  each 
water  spring,  the  hole  is  blown  out  with  steam  or  pumped  out 
with  a  sludge  pump.  Usually  two  or  three  water  springs  will 
be  used;  the  succeeding  springs  are  tamped  up  with  sand  and 
detonated  with  a  battery. 

"Two  exploders  are  always  placed  in  a  hole,  as  it  would  be 
exceedingly  hazardous  to  draw  the  tamping  in  case  of  a  misfire. 
Misfires  with  a  battery  are,  however,  extremely  rare.  Usually 
the  spring  will  not  throw  the  tamping  if  more  than  6  or  7  ft.  are 
used. 

"Blasting.  —  Springing  is  continued  until  it  is  estimated  that 
the  pocket  is  large  enough  to  hold  the  blasting  charge.  The 
charge  is  computed  from  the  number  of  cubic  yards  the  blaster 
estimates  will  be  thrown  out.  The  springing  opens  up  the  rock 
jointing  and  indicates  very  closely  where  the  burden  of  the  shot 
will  cleave  from  the  solid,  and  the  successive  springing  charges 
indicate  the  ratio  of  enlargement  of  the  pocket.  At  least  60  Ib. 
of  black  powder  or  40  Ib.  of  dynamite  should  be  loaded  for  each 
100  cu.  yd.  of  the  shot. 

"The  following  are  typical  springing  and  blasting  charges: 
(1)  A  25-ft.  hole,  burdened  18  ft.,  in  the  bottom  bench  of  a  45-ft. 
cut  —  first  spring,  2  sticks  (60  per  cent,  dynamite);  second 
spring,  4  sticks;  third  spring,  10  sticks;  fourth  spring,  25  sticks; 
fifth  spring,  60  sticks;  sixth  spring,  100  sticks;  seventh,  180  sticks; 


312  ROCK  DRILLS 

blast  charge,  325  Ib.  black  powder.  (2)  A  25-ft.  hole,  burdened 
12  ft.,  in  the  upper  bench  of  a  45-ft.  cut  —  first  spring,  6  sticks 
(60  per  cent,  dynamite);  second  spring,  20  sticks;  third  spring, 
60  sticks;  fourth  spring,  125  sticks;  blast  charge,  325  sticks  (150 
Ib.)  of  40  per  cent,  dynamite. 

"  The  effective  force  of  the  blast  is  a  short  powerful  blow  equiva- 
lent in  length  to  about  one-half  the  diameter  of  the  powder  charge. 
This  blow  is  transmitted  in  all  directions.  In  the  immediate 
vicinity  of  the  powder  charge  the  compression  is  so  great  as  to 
crush  and  pulverize  the  rock.  As  it  expands  toward  the  free 
faces  its  energy  becomes  absorbed  by  the  elasticity  of  the  rock, 
and  the  recoil  from  the  compression  throws  the  rock  out,  the 
propulsion  being  assisted  by  the  backlash  of  the  wave  of  com- 
pression from  the  solid  behind  the  shot.  The  rock  is  heaved 
out  not  so  much  by  direct  propulsion  from  the  seat  of  the  explo- 
sion as  by  the  momentum  of  the  transmitted  shock  which  is 
greatest  near  the  free  faces.  The  natural  rock  jointing  materially 
influences  the  results  of  a  heavy  blast. 

"Conditions  Affecting  the  Blast. —  The  heavy  springing  opens 
up  the  jointing  and  the  blocks  shift  irregularly  on  the  bed  planes, 
often  completely  closing  off  the  drill  hole.  Here  is  one  great 
advantage  of  machine-drilled  holes,  for  owing  to  their  greater 
diameter  they  permit  of  considerable  shifting  before  the  hole  is 
cut  off.  The  effect  of  floors  and  slips  between  the  explosive  and 
the  free  faces  is  to  cause  the  rock  to  cut  off  at  one  of  these  floors 
while  the  rock  around  the  explosive  is  merely  crushed  and  shat- 
tered. These  slips  and  floors  deaden  and  deflect,  or  at  least 
imperfectly  transmit,  the  shock  of  the  explosion.  On  the  other 
hand,  if  the  slips  and  floors  are  behind  and  under  the  blast  charge, 
the  momentum  of  the  rock  ahead  of  the  shot  would  tear  back 
to  these  slips  and  floors,  giving  a  great  deal  more  muck  than  would 
be  expected. 

"The  slips  and  floors  put  a  practical  limit  to  the  size  of  the 
blast.  I  find  that  this  limit  is  reached  with  30-ft.  holes,  burdened 
15  ft.,  and  throwing  out  from  400  to  800  tons  of  muck. 

"The  remark  is  often  made  that  water  is  the  best  tamping  for 
dynamite.  As  a  matter  of  fact,  I  note  that,  in  springing,  water 
tamping  is  always  blown  even  if  the  hole  is  full  of  water,  whereas 
7  or  8  ft.  of  sand  tamping  is  seldom  blown  out  unless  the  rock 
is  very  tough  and  the  bottom  of  the  hole  dead  on  the  solid. 


EXAMPLES  OF  ROCK   DRILL  PRACTICE  313 

"Loading.  —  The  following  precautions  should  be  observed  in 
loading  blast  holes.  The  loading  stick  should  be  a  single  straight- 
grained  stick  1J  in.  in  diameter  at  the  middle,  tapering  to  1  in. 
at  the  ends.  It  is  made  by  dressing  down  a  long  tamarack 
sapling.  Before  loading  a  hole,  put  in  the  loading  stick  for  ten 
minutes  and  see  that  it  is  cold  for  its  entire  length  as  it  is  with- 
drawn, because  a  hole  may  be  cold  on  the  bottom  and  hot  a  few 
feet  above.  After  a  heavy  spring  the  holes  should  be  allowed 
to  cool  for  hours ;  sometimes  the  gases  catch  fire  after  an  explosion, 
and  burn  quietly  for  an  hour  or  more  in  the  hole.  Never  load 
partially  thawed  dynamite,  and  in  loading  a  ragged  hole  do  not 
skin  the  cartridges.  Simply  slit  the  paper  in  two  or  three  places. 
If  loose  dynamite  is  put  in,  it  lodges  in  crevices  along  the  sides 
of  the  hole  and  is  liable  to  be  exploded  by  the  blow  pipe  or  churn 
drill  used  to  draw  the  tamping  after  firing  the  springs.  Use 
exploders  with  lead  wires  as  long  as  the  hole. 

"  Ragged  holes  are  more  easily  loaded  with  black  powder  than 
with  dynamite.  I  have  loaded  holes  in  which  the  springing 
had  shifted  the  rock  so  that  a  loading  stick  could  not  be  shoved 
down,  by  simply  pouring  in  the  powder,  lowering  the  primer 
and  lead  wire  and  then  pouring  down  dry  sand.  Of  course  this 
is  taking  big  chances,  for  the  hole  is  liable  to  plug  up  with  the 
first  keg.  Black  powder  can  be  used  only  when  the  hole  is  dry. 
A  wet  hole  can  often  be  dried  by  firing  a  few  sticks  of  dynamite 
in  the  pocket.  Black  powder  requires  more  tamping  than  dyna- 
mite. Not  only  the  hole  itself  but  all  crevices  showing  in  the 
rock  above  the  blast  should  be  tamped  with  dry  sand. 

' '  I  find  that  three  kegs  of  black  powder  are  equal  to  50  Ib. 
of  40  per  cent,  dynamite.  Neither  dynamite  nor  black  powder 
will  throw  a  good  shot  if  the  rock  has  been  shaken  up  too  much 
by  previous  springing.  With  large  burdens  the  heavy  springing 
opens  up  the  seams  so  much  that  excessive  powder  charges  are 
required  to  make  a  shot;  and  the  explosive  is  liable  to  kick  back 
through  a  seam  and  leave  a  standing  shot.  The  muck  from  a 
very  heavy  blast  is  usually  coarse  and  requires  much  block-holing 
or  bulldozing  before  it  can  be  handled.  The  most  economical 
shots  are  from  holes  16  to  24  ft.  deep  and  burdened  from  12  to 
15  ft.  It  is  very  seldom  that  a  heavy  blast  throws  the  rock  far, 
the  bulk  of  the  muck  being  heaved  out  20  to  50  ft.,  and  very 
rarely  are  any  fragments  thrown  more  than  150  ft. 


314  ROCK    DRILLS 

"  Cost  of  Excavating.  —  In  the  accompanying  table  is  given  the 
cost  of  excavating  and  moving  a  cubic  yard  (4400  Ib.)  of  red 
granite,  steam  drills  being  used  for  drilling  and  stone  boats  and 
pole  tracks  for  hauling  out  the  rock,  the  average  hight  of  the  cut 
being  46  ft.  and  the  average  haul  500  ft.  The  item  of  general 
expense  covers  the  cost  of  hauling  in  the  outfit  and  of  building  log 
camps  for  men,  etc.  Aside  from  this  item  the  actual  cost  of 
breaking  and  hauling  the  rock  is  87c.  per  cu.  yd.,  or  a  little  less 
than  40c.  per  ton." 

COST  OF  EXCAVATING  RED  GRANITE 

Per  Cu.  Yd. 
Breaking. 

Drilling  blast  holes $0.048 

Labor,  springing  and  loading  holes 0.030 

Dynamite    0.084 

Black  powder  0.024 

Wire  exploders   0.008 

$0.194 
Handling  the  Broken  Rock. 

Block-holing  and  bulldozing $0.104 

Loading 0.308 

Haulage 0.165 

$0.577 
General  expenses    .    0.250 


Total    $1.021 


XIV 
ROCK   DRILL  TESTS   AND   CONTESTS 

NOTES   ON   ROCK  DRILL  TESTS  AND  THE  POSSIBLE  LINES  OF 
FUTURE  DEVELOPMENT  OF  DRILLING  MACHINES 

IT  has  been  very  truly  said  that  the  only  test  to  which  a  rock 
drill  can  be  subjected  with  any  fairness  is  to  put  it  to  work 
under  mining  conditions  for  an  extended  period.  I  have  already 
emphasized  the  importance  of  wear  as  bearing  on  rock  drill 
efficiency,  also  the  mining  conditions  and  treatment  as  effecting 
their  design. 

There  are  many  types  of  machines  that  we  know  stand  this 
test  and  do  an  average  amount  of  boring.  It  might  reasonably 
be  urged  that  we  wish  to  know  other  things  about  these  drills, 
which,  though  secondary  matters,  are  important  in  themselves. 
It  is  difficult  to  keep  a  record  of  actual  footage  bored  in  working 
time  over  such  a  period.  We  might  wish  to  know  as  among 
any  number  of  makes  of  rock  drill  what  is  the  relative  air  and 
water  consumption;  the  relative  boring  speed  under  similar 
conditions;  the  relative  time  of  actual  boring  to  the  total  working 
time;  the  relative  efficiency  in  boring  dry  holes  and  wet  down- 
holes;  the  relative  efficiency  with  different  air  pressures;  the 
relative  percentage  of  energy  supplied  to  the  drill  that  is  turned 
into  actual  work  in  boring  rock;  the  reason  for  any  difference,  if 
found;  the  number  of  blows  per  minute,  and  what  is  the  minimum 
difference  in  gage  that  can  be  employed  in  following  sizes  of  steel. 
The  relative  cost  of  up-keep  we  can  learn  from  mine  account  books. 

A  test  to  give  all  this  information  has  never  yet  been  carried 
out.  It  would  involve  an  immense  amount  of  labor.  Enough 
has  been  done  to  show  how  such  information  should  be  sought. 
The  most  thorough  tests  ever  made  of  a  rock  drill  were  those 
conducted  on  the  Torpedo  baby  "Corliss  Valve  Drill,"  by  Hol- 
loran  &  Hamilton. 

Determining  Number  of  Blows.  —  To  determine  the  number 

315 


316  ROCK   DRILLS 

of  blows  struck  per  minute,  a  roll  of  stout  Manila  paper  was 
mounted  on  a  vertical  spindle,  and  pulled  rapidly  in  front  of  the 
bit  so  as  to  be  punched  by  it.  The  paper  was  unwound  for  15 
seconds;  the  number  of  holes  multiplied  by  four  gave  number 
of  blows  struck  per  minute.  The  machine  was  2J-in.  cylinder- 
diameter,  with  a  stroke  from  4£  to  If  in.  long.  The  number  of 
blows  struck  per  minute  varied  from  540  at  50  Ib.  pressure  to 
896  at  99-lb.  pressure;  at  60  Ib.  the  number  was  566;  at  70  Ib., 
626;  and  at  80  Ib.,  660.  Shortening  the  stroke  to  2f  in.  greatly 
increased  the  number  of  blows  per  minute.  At  60  Ib.  the  number 
was  829;  at  70  Ib.,  866;  at  80  Ib.,  935;  and  at  90  Ib.,  993. 

Air  Consumption.  —  This  was  measured  by  connecting  the 
exhaust  to  a  100-gal.  tank  as  a  receiver,  and  then  carrying  the 
air  to  two  300-light  wet  gas  meters.  In  the  measurement  of 
the  flow  of  gas  the  product  of  the  absolute  pressure,  p,  by  volume,  v, 
divided  by  absolute  temperate,  t,  is  a  constant ;  pv  =  constant.  If 
P  and  T  are  kept  constant  the  quantity  discharged  will  vary  as  the 
volumes,  and  if  P  and  T  are  known,  the  quantity  can  be  computed. 
The  gas  meter  is  arranged  with  a  series  of  chambers  which  are  alter- 
nately filled  and  emptied  of  gas.  Air  consumption  was  39  cu.  ft. 
per  minute  at  70  Ib.  pressure;  47  at  80  Ib.;  37  at  60  Ib.;  and  33 
at  50  Ib.  These  results  were  checked  by  measuring  volumes  in 
cylinder,  taking  temperature  and  number  of  blows  per  minute. 

Determination  of  Absolute  Force  of  Blow  with  Varying  Length 
of  Stroke.  —  The  piston  and  drill  were  allowed  to  fall  freely  and 
indent  a  lead  bar  placed  on  an  anvil.  The  hights  of  fall  varied, 
and  the  indentation  was  measured.  The  indentation  produced 
by  the  rock  drill  working  at  a  certain  pressure,  with  strokes  of 
4J  in.,  3J  in.,  2  in.,  and  If  in.,  was  then  compared  with  them,  each 
being  measured  by  a  vernier  micrometer.  Trie  foot-pounds  of 
energy  developed  by  a  body  of  known  weight  falling  a  known 
distance  can  easily  be  calculated,  V  =  \/2  gh.  The  foot-pounds 
per  minute  =  21  Ib.  X  hight  X  number  of  blows  per  minute. 
The  If -in.  stroke  gave  a  vis  viva  for  a  single  blow  of  46.2  foot- 
pounds. The  4J-in.  stroke  gave  53.2  foot-pounds.  With  the 
If -in.  stroke  these  was  no  cushioning  effect,  whereas  there  was 
some  with  the  4J-in.  stroke.  Yet  in  practice  it  would  appear  that 
the  added  force  of  blow  gained  by  a  long  stroke  does  not  make 
up  for  the  loss  of  number  of  blows  per  minute.  The  authors  say: 
"It  has  been  found  that  a  greater  number  of  less  powerful  blows 


ROCK   DRILL  TESTS  AND  CONTESTS  317 

does  more  work  than  a  smaller  number  of  greater  blows."  Yet  it 
will  be  observed  that  most  modern  rock  drills  are  designed  on  ex- 
actly the  opposite  principle  —  the  stroke  being  made  long  to  kick 
mud  from  out  the  bottom  of  the  hole.  The  force  of  a  drill  on  rock 
cannot  be  exactly  calculated  as  the  force  will  be  different  for  differ- 
ent substances,  each  having  a  different  resistance  to  indentation. 
The  writers  say  the  consideration  of  the  different  rate  at 
which  the  number  of  blows  per  minute  increase  with  rise  of  air 
pressure  "  suggests  the  value  of  a  careful  investigation  of  the 
character  of  every  rock  drill  and  the  condition  under  which  it 
will  do  the  best  work."  The  assumption  that  an  increased  pres- 
sure means  increased  work  is  not  always  true.  The  best  pres- 
sure indicated  for  this  drill  the  authors  consider  to  be  100  Ib. 
With  hollow  steel  and  water  injection  it  might  be  run  on  a  2-in. 
stroke  to  greatest  advantage. 

DRILL  TESTS 

Mr.  H.  P.  Griffiths  1  gives  particulars  regarding  trials  carried 
out  in  1902.  The  machines  tried  were  the  Climax  air  and  tappet 
valve,  Rio  Tinto  drill,  Holman  drill,  Champion  Eclipse  drill. 
The  machines  had  to  bore  two  holes  on  a  faced  rock.  The  quan- 
tity of  air  consumed  was  computed  from  dimensions  of  compressor, 
number  of  strokes,  exact  measurement  of  receiver,  due  correc- 
tions being  made  for  temperature.  The  following  were  some  of 
the  conclusions  arrived  at  as  a  result  of  the  test: 

(1)  Cross-bit  bores  further  than  chisel  bit  and  bores  a  hole 
of  larger  capacity.  (2)  The  wear  is  less  on  cross-bits  than  on 
chisel  bits.  (3)  Air  valves  are  more  economical  to  work  than 
tappet  drills.  (4)  All  drills,  except  the  Eclipse,  had  exhaust 
ports  of  too  small  area.  (5)  Within  reasonable  limits  the  fewer 
the  number  of  blows  per  minute  the  better  the  results.  It  is 
not  stated  how  this  conclusion  was  arrived  at.  (6)  All  valves 
leaked  owing  to  negative  lap.  (7)  Lightness  of  reciprocating 
part  is  necessary.  (8)  The  effectiveness  of  blow  depends  more 
upon  the  velocity  than  upon  the  mass  of  the  reciprocating  part. 
These  last  two  conclusions  appear  contrary  to  theory  and  practice. 
Theoretically  the  kinetic  energy  of  the  blow  =  MV2,  where  M  = 
mass  and  V  =  velocity.  Doubling  the  velocity  increases  the 
energy  of  blow  four  times,  while  M  must  be  increased  four  times 
1  Journal  Mech.  Eng.  Assn.  of  South  Africa. 


318  ROCK  DRILLS 

to  accomplish  the  same  result.  The  air  consumption  for  an  air 
pressure  falling  from  75  to  50  Ib.  for  these  drills  showed:  3^-in. 
drill,  178.9  Ib.;  3f-in.  drill,  130.4  Ib.;  and  a  3-in.  drill,  118.3  Ib. 

In  1903  a  series  of  tests  was  carried  out  in  Johannesburg  by 
Messrs.  Carper,  Goffe,  and  Docharty.  The  results  were  recorded 
in  the  Journal  of  the  Mechanical  Engineers'  Association  of  South 
Africa. 

All  holes  were  drilled  by  3-in.  to  2-in.  diameter  star  bits,  ver- 
tically, into  a  block  of  granite  4i  X  4i  X  2  ft.  Two  air  receivers 
had  a  capacity  of  756.6  cu.  ft.  Machines  were  rigidly  set  up. 
Each  run  was  conducted  as  follows:  The  compressor  was  worked 
until  the  gage  on  the  receivers  showed  the  required  starting 
pressure  (say  80  Ib.).  The  stop  valve  was  then  shut,  closing  con- 
nection with  the  compressor.  The  machine  being  in  position  on 
the  bar  and  all  ready  was  then  started,  and  drilling  continued  until 
the  terminal  pressure  of  that  stage  (say  70  Ib.)  was  shown  on  the 
receiver.  The  machine  was  then  stopped  and  the  depth  of  the 
hole  carefully  measured  and  recorded.  The  times  of  starting  and 
stopping  were  taken,  and  lengths  of  any  stoppages  during  the  run 
noted,  the  net  time  of  the  run  being  thus  found.  The  machine 
was  then  restarted  at  70  Ib.  pressure  and  run  to  60  Ib.  and  again 
measured,  and  so  on  for  each  stage  down  to  35  Ib.  Before  start- 
ing a  hole  the  bit  was  carefully  measured.  On  starting  and 
stopping  each  stage  of  the  run  the  pressure  and  temperature  of 
the  air  passing  through  the  machine  was  observed  as  well  as  the 
atmospheric  pressure  shown  by  barometer. 

It  was  intended  originally  to  go  through  all  the  stages  of  pres- 
sure for  each  drill  with  one  hole,  but  the  stone  was  too  thin  and 
this  scheme  had  to  be  modified;  the  plan  was  adopted  of  running 
the  first  two  stages  only,  viz.,  80  Ib.  to  70  Ib.,  and  70  Ib.  to  60  Ib.,  in 
one  hole,  then  starting  a  new  hole  with  a  new  drill  bit  and  running 
three  stages,  viz.,  60  Ib.  to  50  Ib.,  50  Ib.  to  40  Ib.,  and  40  Ib.  to  35  Ib. 

Calculation  of  Volume  of  Air.  —  The  following  is  the  method 
adopted  for  calculating,  from  the  observations  taken,  the  quan- 
tity of  air  used  by  the  drills: 

The  standard  of  free  air  at  24.8  in.  barometer  with  70°  F.  tem- 
perature was  adopted.  Johannesburg  is  6000  ft.  above  sea  level. 

The  pressure  in  pounds  per  square  inch,  due  to  pressure  of 
atmosphere,  was  found  by  multiplying  the  barometric  reading  in 
inches  by  0.4908. 


ROCK   DRILL  TESTS  AND  CONTESTS  319 

The  formula  Vl  =  V  X  — 

t\  X  1 

where 

V   =  Volume  of  1  cu.  ft.  at  standard  pressure,  and  tem- 
perature =  T 

Vi  =  Volume  of  1  cu.  ft.  standard  free   air   at  new  pres- 
sure and  temperature 

P   =  Standard  pressure  (absolute)  =  12.17184  Ib. 
pt  =  New  pressure  (absolute) 
T   =  Standard  temperature  (absolute)  =  531°    F. 
TI  =  New  temperature  (absolute) 

was  used  to  find  the  volume  of  1  cu.  ft.  of  standard  free  air  at 
any  other  pressure  and  temperature. 

Then  taking  the  required  observations  for  the  stage  80  to  70 
Ib.,  and  working  them  out  as  an  example,  we  have,  at  start  of 
run: 

Gage  pressure  =  80  Ib. 
Barometer  =  24.95  =  12.24546  Ib. 
Temperature  =  100°  F. 
Pi  =  92.24546 
Ti  =  561 
Therefore 

12.17184  X  561 
F'  =  92.24546  X  531 

The  cubic  contents  of  the  receiver,  as  stated,  was  756.5  cu.  ft. 
Evidently  then  the  amount  of  standard  free  air  contained 
will  be  — 

5426-8  cu- ft-   >:,.     : 

Take  next  the  conditions  at  finish  of  run  — 

Gage  pressure  =  70  Ib. 

Barometer  =  24.95  =  12.24546 

Temperature  =  99°  F. 

Pi  =  82.24546 

Ti  =  560 
Therefore, 

12.17184  X  560 


82.24546  X  531 


=  0.15607  cu.  ft. 


320 


ROCK  DRILLS 


and  the  free  air  contained 
756.5 


=  4847.2  cu.  ft. 


0.15607 

The  amount  of  air  consumed  during  the  run  will  be  the  differ- 
ence between  the  contents  at  start  and  finish  - 
5426.8  -  4847.2  =  579.6  cu.  ft. 

Air  Consumption. —  The  average  of  thirteen  3j-in.  drills  gave 
the  following  results  as  to  quantity  of  air  used  at  various  pressures: 


Cubic  Feet 

Mean  Pressure  Lb.  per  Sq.  In. 

Ratio  of  Boring  per  Min. 
Inches 

124 

75 

1.3 

117 

65 

1.1 

100 

55 

1.0 

70 

45 

0.6 

60 

37^ 

0.5 

Rifling.  —  These  tests  yielded  much  valuable  information,  but 
many  of  the  results  and  the  deductions  drawn  from  them  have 
to  be  accepted  with  caution.  Most  of  the  machines  that  in  prac- 
tical work  give  no  trouble  were  reported  as  rifling  the  hole  badly 
and  refusing  to  rotate.  The  drill  bits  used  were  not  of  uniform 
quality.  Undoubtedly  the  chief  mistake  made  was  in  starting 
holes  with  machines  drilling  at  full  speed.  This  was  undoubtedly 
the  cause  of  most  of  the  rifling.  No  mine  would  think  of  start- 
ing a  hole  in  hard  rock  in  this  way,  as  the  vibration  set  up  makes 
the  bit  strike  the  mouth  and  sides  of  holes. 

Table  II  shows  particulars  of  runs  carried  out  with  3J-in. 
drills  of  three  types:  Air  valve  machine  Slugger;  tappet  valve  Lit- 
tle Giant;  auxiliary  valve  Ingersoll-Sergeant.  For  comparative 
purposes  the  run  of  the  Ingersoll  machine  was  spoiled  by  rifling. 
The  figures  from  a  similar  run  of  a  3-in.  Leyner  hammer  drill 
are  shown  by  comparison.  Why  this  drill  did  not  show  as  high 
an  efficiency  as  the  piston  drills  is  not  known.  These  figures  are 
interesting  in  showing  the  increase  of  drilling  speed  due  to 
increased  air  pressures  with  corresponding  increase  of  air  con- 
sumption. It  is  interesting  to  note  that  at  present  few  Slugger 
machines  are  working  in  this  field  and  also  comparatively  few 
tappet  machines. 


ROCK   DRILL   TESTS  AND   CONTESTS 

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322 


ROCK  DRILLS 


TABLE  II. 


^ame  Q£  drill            

INGERSOLL                                                   3J 
Bore  3J  in.     Stroke  6}  in. 

SLUGGER 
Bore  3J  in.; 

gize                         

Weight  
Condition                          

277  Ibs. 
New,  from  Robinson  G.  M.  Co. 

321  Ibs. 
New,    from 

Reference  No.  of  run     

1 

1 

29 

29 

29 

Totals 

48 

48 

Air  pressures  (gage),  Ib.  per 
aq.  in  

80.70 

70.60 

60.50 

50.40 

40.35 

80.35 

80.70 

70.60 

45  Ibs.  fall 

Size  of  bit,  in.         

3 

3 

3 

3 

3 

3 

3 

3 

Net  time  of  run    min 

6.083 

3.25 

5.416 

7.8 

4.416 

26.965 

7.166 

7.582 

Depth  drilled  in. 

7 
1.15 

5 
1.54 

6.875 
1.26 

5.625 
0.72 

5.75 
0.62 

27.25 
1.01 

10.625 
1.48 

8.375 
1.10 

Depth  drilled  per  minute,  in. 

Capacity  of  hole  drilled,  cu. 

in  

49.48 

35.34 

48.59 

39.76 

19.44 

192.61 

75.10 

59.20 

Equivalent  free  air  used  at 

70°  Fah.,  24.8  in.  barom- 

eter, total  cu.  ft  

642.7 

611.4 

620.3 

610.3 

301.8 

2786.5 

653.3 

643.9 

Equivalent  free  air  used  per 

in   drilled   cu.  ft. 

91.8 

122.3 

90.2 

108.5 

109.7 

102.2 

61.5 

76.9 

Equivalent  free  air   used  per 

min.  run,  cu.  ft  

105.6 

188.1 

114.5 

78.2 

68.3 

103.3 

91.1 

84.9 

Equivalent  free  air  used  per 

cu  in  of  hole,  cu.  ft. 

12.99 

17.30 

12.76 

15.35 

15.52 

14.46 

8.70 

10.80 

Notes  on  run 

M  a  c  h  i  ne  ran 

Rotation  bad  from  start. 

Very  satisfac- 

short  stroke. 

Machine    sluggish  on 

t  ory     run. 

Rotating  badly. 

return  stroke. 

Drilled     good 

Drill  bent    and 

round   hole. 

hole  rifled,  caus- 

No stop  from 

ing    drill     to 

drill   sticking. 

bind   and  stick 

in  hole.  Consid- 

ered     machine 

should   be    run 

again. 

A  trial  was  also  made  with  a  2J-in.  Slugger  machine  (Table  I) 
using  different  sized  bits.  The  results  are  interesting  as  showing 
how,  other  things  being  equal,  speed  of  drilling  varies  inversely 
as  the  area  of  hole  excavated  within  certain  limits.  It  shows  the 


ROCK   DRILL  TESTS  AND  CONTESTS 
ROCK  DRILL  TESTS 


323 


Stroke  6J  in. 

Agents  (Fraser  &  Chalmers). 


3t 


LEYNER  —  WATER 

Bore  3  in. ;  Stroke  3  in. 

156  Iba. 

New,  from  Agents  (Leyner  &  Co.). 


27 

27 

27 

Totals 

19 

19 

20 

20 

Totals 

60.50 

50.40 

40.35 

80.35 

80.70 

70.60 

80.70 

70.60 

80.60 

45  Ibs.  fall 

20  Ibs.  fall 

3 

3 

3 

3 

2A 

2  A 

2| 

21 

2i'B  21 

8.550 

11.666 

6.416 

41.381 

5.333 

6.166 

7.0 

6.5 

25.0 

8.375 

6.375 

2.812 

5  36.562 

8.0 

8.5 

8.25 

8.125 

33.125 

0.98 

0.54 

0.44 

0.88 

1.50 

1.37 

1.21 

1.25 

1.32 

50.29 

45.06 

19.88 

258.44 

26.73 

29.38 

30.14 

28.82 

114.08 

653.6 

616.8 

296.2 

2863.8 

614.6 

621.7 

608.8 

609.9 

2455.0 

78.0 

96.7 

105.3 

78.3 

76.8 

73.1 

71.6 

75.0 

74.1 

76.4 

52.8 

46.1 

69.2 

115.2 

100.8 

86.9 

93.8 

98.2 

11.04 

13.68 

14.90 

11.08 

23.0 

21.89 

20.2 

21.16 

21.52 

Machine    run    loose    in 

Excessive  vibra- 

Repeated   same    stage 

cradle.     Hole  slightly 

tion.      Hole 

run    with    drill    bar 

rifled.    No  stoppage 

b  a  d  ly  rifled. 

fast.      Fair  run,   no 

from  drill  sticking. 

D  r  ill    bar 

stoppages. 

slightly  loose 

at  start. 

importance  of  keeping  the  difference  of  following  gages  of  bits 
as  small  as  possible,  and  drilling  the  hole  of  the  minimum  size 
required  to  hold  sufficient  charge  to  break  the  rock. 


324  ROCK  DRILLS 

Gillette  gives  the  following  summary  of  the  results  of  tests 
carried  out  at  the  Rose  Deep  mine,  South  Africa,  by  Major 
Seymour: 

Test  of  Air  Consumption  at  the  Rose  Deep  Mine.  —  A  six-hour 
run  at  the  Rose  Deep  Mine,  South  Africa,  showed  the  following 
results  for  31  drills:  The  compressed  air  averaged  70  Ib.  per  square 
inch  and  each  3J-in  drill  consumed  81  cu.  ft.  of  free  air  per  minute, 
including  all  leakage  of  pipes  (there  was  less  leakage  than  is  com- 
mon in  mines).  Each  drill  required  43  Ib.  of  coal  per  hour, 
to  supply  this  compressed  air;  and  each  pound  of  coal  developed 
3.4  h.p.  per  hour,  by  the  indicator  on  the  steam  engine,  evaporat- 
ing 6.74  Ib.  of  water  from  212°  F.  The  average  h.p.  of  the  com- 
pressor engine  was  12.7  i.h.p.  per  drill;  but  all  the  drillers  were 
trying  to  make  a  record  and  accomplish  in  six  hours  an  amount 
of  drilling  that  ordinarily  took  eight  hours.  It  was  an  efficient 
steam-power  plant,  as  is  seen  by  the  fact  that  3.4  h.p.  were  devel- 
oped with  each  pound  of  coal.  The  power  plant  was  a  vertical 
King-Reidler  compound  steam  engine  and  double  stage  air 
compressor  with  two  boilers  of  the  horizontal  return  tubular 
type.  The  engine  developed  393  i.h.p.  and  had  a  mechanical 
efficiency  of  86  per  cent.  There  were  several  sizes  of  machine 
drills  used,  but  they  were  all  reduced  to  the  3j-in.  size  as  standard 
by  the  test  of  filling  the  cylinders,  ports,  etc.,  with  water  and 
ascertaining  the  volume  of  water  for  each  drill  cylinder.  This 
showed  the  rating  of  the  drills  in  air  consumption  to  be  as  fol- 
lows: 

Relative  Air 
Consumption 

2j-in.  drill    0.445 

3^-in 1.000 

3^-in 1.069 

3f-in.   .  1.123 

The  31  drills  averaged  4.5  ft.  of  hole  drilled  per  hour  for  the 
6-hour  run;  one  3J-in.  drill  making  52  ft.  of  hole  in  six  hours;  drill- 
ing four  dry  holes.  Comparing  the  consumption  of  81  cu.  ft.  of 
free  air  per  minute,  at  70  Ib.,  with  the  average  of  120  cu.  ft.  (at 
average  of  70  Ib.)  given  in  the  first  two  items  in  the  table  on 
page  321,  gives  a  fair  idea  of  the  difference  between  a  long  test 
using  a  number  of  drills,  and  a  short  test  of  one  drill. 


ROCK   DRILL  TESTS  AND  CONTESTS 


325 


Horse-Power  Tests.  —  M.  K.  Schweder  in  1897  made  experi- 
ments showing  that  the  h.p.  required  at  65  Ib.  air  pressure  was 
17.8  per  drill,  but  he  assumed  that  all  drills  were  running. 

Mr.  C.  E.  Hut  ton,  in  a  paper  read  before  the  South  African 
Association  of  Engineers,  gives  the  accompanying  Table  III:_ 

TABLE  III.     ROCK  DRILL  TESTS 
Van  Ryn  Gold  Mines  Estate,  Ltd. 


1 

£ 

*]t 

W 

M 

Name  of 
Machines 

Average  Time 
Worked  per 
Machine 

Average  Depth 
Drilled  per 
Machine 

Average  Depth 
Drilled  per 
Machine  per  Min 

A 

160.5 

97.5 

258 

Minutes 

Inches 

Inches 

B 

64.5 

46.25 

110.75 

Ingersoll 

99 

•1  f\    O 

267 

C 

154 

94.75 

248.75 

5  machines 

~ir  =19.8 
o 

~5~=  53.4 

2.69 

D 

162 

91 

253 

E 

157 

89.75 

246.75 

Hercules, 

115-6 

288.5 

7  machines 

_      =  lb.5 

7 

2.49 

F 

153 

89.75 

242.75 

G 

155.5 

100 

255.5 

Slugger, 

175 

414.5 

H 

167 

92 

259 

8  machines 

—  =  21.87 

~8~~51'8 

2.37 

I 

111.5 

67.25 

178.75 

J 

165 

98.5 

263.5 

Holman, 

55.75 

165 

2  machines 

—  —  =  27.87 

—  =82.5 

2.96 

K 

90 

54.5 

144.5 

L 

165 

97.5 

262.5 

Average  i.h.p 223.9 

Revs,  of  compressor  during  test  for  one  hour.     2,639  revs. 
Volume  of  free  air  taken  in  at  compressor .  . .  100,492  cu.  ft. 
Loss  in  air  column  and  receivers  in  free  air 

(see  separate  test)    16,905  cu.  ft. 


40.5  leakage  loss 


Balance  for  use  at  drills   83,587  cu.  ft. 

83,587X85 


Corrected  to  sea  level  

Volume  at  75  Ibs.  pressure  per  sq.  in 


100 
71,050X14.7 


=  71,050  cu.  ft. 
=  11,645  cu.  ft. 


75+14.7 

Mr.  Hutton  also  states  that  "the  late  Mr.  L.  I.  Seymour,  in 
his  paper  on  the  tests  of  a  King-Riedler  air  compressor,  read  before 


326  ROCK  DRILLS 

this  Association,  showed  that  the  average  i.h.p.  per  drill  was  12.72 
and  the  total  footage  drilled  in  six  hours  840;  to  get  this  footage 
of  840,  the  compressor  had  to  exert  continuously  over  the  whole 
six  hours  373  i.h.p.,  and  making  a  comparison  with  the  Van  Ryn 
test  of  one  hour,  we  get  the  following: 

Rose  Deep,  373  i.h.p.  exerted  for  one  hour  to  drill  140  ft. 

Van  Ryn,  227  i.h.p.  exerted  for  one  hour  to  drill  94.5  ft. 

or,  again, 

Rose  Deep  1,  i.h.p.  exerted  for  one  hour  to  drill  0.3780  ft. 

Van  Ryn  1,  i.h.p.  exerted  for  one  hour  to  drill  0.4163  ft. 
Therefore,  if  the  Van  Ryn  drills  were  working  full  strength  one- 
third  of  their  time  and  accomplished  practically  the  same  footage 
as  the  Rose  Deep,  one's  natural  conclusions  would  be  that  the 
Rose  Deep  drills  ran  only  about  one-third  of  the  time.  The 
enormous  fluctuation  of  the  air  pressure  shown  by  Mr.  Seymour 
also  goes  to  prove  that  the  drills  must  have  at  times  drawn  from 
the  air  capacities  to  such  an  extent  that  although  the  compressor 
was  running  its  hardest,  the  pressure  could  not  be  maintained; 
therefore,  instead  of  a  drill  absorbing  12.72  i.h.p.  for  six  hours, 
a  drill  with  its  proportion  of  pipe  loss,  etc.,  really  absorbs  some- 
thing like  37  i.h.p.  for  two  hours. 

"Referring  to  test  sheet,  Table  III,  which  gives  details  of 
i.h.p.  and  certain  other  particulars  regarding  work  done  by  the 
rock  drills  and  the  air  consumption  by  them,  it  will  be  seen  that 
over  a  test  of  one  hour  made  with  22  machines  running,  the  i.h.p. 
of  the  air  compressor  averaged  227,  although  the  actual  running 
time  of  the  machines  only  averaged  20.2  minutes  out  of  the  60. 
It  must  be  remembered  that  these  results  were  obtained  at  a 
time  when  it  was  positively  known  that  there  were  no  leaks  of 
any  noticeable  magnitude  in  the  air  mains  either  on  surface  or 
underground,  and  that  the  machines  were  in  good  condition; 
therefore  it  may  be  taken  that  the  conditions  were  somewhat 
better  than  would  be  found  in  the  average  practice. 

"The  short  time  actually  run  by  the  machines  out  of  a  pos- 
sible 60  minutes  shows  how  large  a  percentage  of  the  time  the 
machines  were  off  for  changing  drills,  shifting  positions  of  machines, 
etc.,  and  when  it  is  considered  that  notwithstanding  all  these 
stoppages  and  the  short  acutal  running  time  of  the  machines, 
it  was  necessary  to  continuously  exert  an  average  of  227  i.h.p. 


ROCK  DRILL  TESTS  AND  CONTESTS  327 

on  the  air-compressor  steam  cylinders,  it  can  be  realized  what 
amount  of  power  would  have  been  required  assuming  that  the 
whole  of  the  machines  had  been  run  continuously  through  the 
trial  hour. 

"This  is,  of  course,  to  assume  an  impossible  condition,  but 
it  is  useful  to  realize  that  if  the  machines  could  be  run  continu- 
ously under  the  same  conditions  as  in  the  test,  that  is,  leaving 
the  friction  and  leakage  of  the  pipe  lines,  machines  and  compressor, 
with  the  same  proportionate  losses  through  drop  of  temperature, 
it  would  have  been  necessary  to  develop  about  619  i.h.p.  during 
the  test  to  maintain  a  constant  air  pressure.  On  this  basis  the 
i.h.p.  required  on  the  compressor  per  rock  drill  run  continuously 
in  the  mine  would  be  28,  which  figure  therefore  has  been  adopted 
at  the  Van  Ryn  as  the  prime  basis  for  distribution  of  power  to 
rock  drills.  It  was,  however,  considered  that  the  4:est  conditions 
might  have  been  superior  to  the  ordinary  working  conditions, 
and  it  was  resolved  to  adopt  a  figure  of  32  i.h.p.  as  representing 
the  power  developed  in  the  steam  cylinders  of  the  compressor 
to  run  one  drill  in  the  mine;  this  figure,  of  course,  to  cover  all  the 
losses  of  the  compressor,  air  mains,  drop  in  air  temperature,  and 
machine  inefficiencies." 

Losses  in  Compressed  Air.  —  It  will  be  noted  that  Mr.  Hutton 
found  leakage  losses  to  be  40.5  per  cent.  This  large  figure  may 
be  compared  with  a  recent  test  at  Meyer  &  Charlton  mine  when 
other  losses  were  only  5  per  cent.,  both  being  old  mines. 

Regarding  air  consumption,  E.  C.  Reybold  makes  the  fol- 
lowing remarks:  "This  shows  the  amount  of  power  thrown  away 
by  the  fact  that  the  drill  exhausts  air  at  full  pressure.  In  order 
to  secure  as  much  power  as  possible  from  a  given  weight  of  drill, 
it  is  necessary  to  use  the  air  non-expansively,  and  at  the  end 
of  each  stroke  a  volume  of  compressed  air  equivalent  to  the 
volume  of  the  cylinder  is  discharged  into  the  atmosphere.  The 
energy  thus  wasted  is  measured  by  the  power  required  to  com- 
press to  the  given  pressure  a  sufficient  volume  of  free  air  to  make 
a  volume  under  pressure  equal  to  the  contents  of  the  cylinder. 
This  in  cubic  feet  per  minute  for  a  3i-in.  drill  of  6^-in.  stroke, 
350  strokes  per  minute,  operating  at  90-lb.  pressure,  the  diameter 
of  the  piston  rod  being  If  in.,  is  as  follows:  Area  of  cylinder, 
8.29  sq.  in.;  area  of  piston  rod,  2.07  sq.  in.;  volume  of  cylinder, 
forward  stroke,  53.38  cu.  in.;  volume  of  cylinder,  back  stroke, 


328 


ROCK   DRILLS 


34.21  cu.  in.;  total  displacement  at  350  strokes,  30,831  cu.  in.,  or 
17.84  cu.  ft. 

"The  quantity  of  free  air  required  to  make  17.84  cu.  ft.  at 
90-lb.  pressure,  together  with  the  horse  power  required  at  vari- 
ous altitudes,  assuming  perfect  cooling,  with  two-stage  com- 
pression, is  about  as  follows: 


Altitude 

Free  Air  Required 
Cu.  Ft. 

H.  P.  Required  to 
Compress  100  Cu.  Ft. 

Total   H.  P.  Required 

Sea  level  
5  000  ft.  . 

125 

149 

14.7 

13.45 

18.37 

20.04 

10,000  ft  

179 

12.33 

22.07 

"This  gives  the  loss  occasioned  by  exhausting  at  full  pressure. 
The  total  theoretical  horse-power  that  it  is  possible  to  transmit 
to  the  rock  (forward  stroke  only)  equals  8.29  sq.  in.  X  90  Ib.  per 
square  inch  X  190  ft.  per  minute  equals  141,729  foot-pounds  per 
minute,  or  4.29  horse  power. 

"It  will  thus  be  seen  that,  when  theoretically  considered,  it 
is  possible  to  convey  into  actual  work  not  more  than  10  to  20  per 
cent,  of  the  power  used  in  compressing  the  air.  When  the  losses 
from  radiation  from  the  air  receiver  and  air  pipe  are  considered, 
together  with  the  friction  of  the  air  in  passing  through  the  pipes, 
as  well  as  the  friction  in  the  air  drill,  loss  of  air  from  leaky  valves, 
etc.,  it  will  be  realized  why  so  little  of  the  power  expended  at  the 
compressor  is  actually  transmitted  into  work  at  the  breast." 

Konomax  vs.  Ingersoll.  —  In  1907  a  test  was  conducted  by 
J.  A.  McGeorge  (the  Journal  of  the  Transvaal  Institute  of 
Mechanical  Engineers)  between  a  3-in.  Konomax  drill  and  a 
3i-in.  Ingersoll-Sergeant  drill.  The  test  was  carried  out  in  the 
same  manner  as  those  by  Messrs.  Docharty  and  Goffe.  It  was 
open  to  the  same  objections,  no  holes  being  deeper  than  about 
11  in.  and  the  average  about  6  in.  Some  of  the  results  obtained 
are  of  interest  in  comparison  with  those  already  given.  (See 
Table  IV  on  opposite  page.) 

It  will  be  noted  that  the  Konomax  excavated  one  cubic  inch  of 
rock  for  expenditure  of  8.4  cu.  ft.  of  free  air.  For  about  the  same 
pressures  the  Slugger  drill  in  the  1903  tests  used  about  10  cu.  ft. 
of  air.  It  will  be  seen  that  the  Ingersoll  used  13.8  as  against 


ROCK   DRILL  TESTS  AND   CONTESTS 


329 


TABLE  IV.     DRILL  TEST,  KONOMAX  vs.  INGERSOLL 


Name  of  Drill 

Size  of  Bit 
About 

Air 
Pressure 
per  Sq.  In. 

Average 
Drilling 
Inches 
per  Min. 

Cu.  Ft. 

Air  (Free) 
Used  per 
Linear 
Inch 
Drilled 

Free  Air 
Cu.  Ft. 
Used  per 
Cu.  In. 
Excavated 

Cu.  Ft. 
Free  Air 
Used  per 
Minute 

Konomax  . 

2£ 

80.7 

1.62 

41.7 

8.2 

66.2 

Ingersoll  
Konomax  
Ingersoll  .  ... 

2* 
2£ 
2£ 

80.7 
70.6 
70.6 

1.53 
1.55 

1.78 

69.5 
38.3 
65.8 

12.8 
8.0 
13.8 

104.9 
57.9 
112.3 

Konomax  
Ingersoll  

2| 
2| 

60.5 
60.5 

1.26 
1.67 

36.8 

58.2 

9.2 
14.5 

45.5 
93.2 

14.46.  Several  obvious  analogies  show  the  results  obtained  to 
be  not  altogether  reliable.  For  instance,  the  Ingersoll  machine 
is  shown  to  drill  faster  at  70  and  60  Ib.  and  to  use  more  air  at 
70  than  at  80  Ib.  pressure.  About  the  same  time  a  test  was  made 
starting  with  holes  7  in.  deep  and  drilling  to  a  depth  of  15  to  20 
in.  The  air  pressure  was  50  Ib.  and  bits  2i-in.  diameter.  The 
result  obtained  was  a  drilling  speed  of  1.09  in.  per  minute  for 
the  Konomax  drill  and  1.7  in.  per  minute  for  the  Ingersoll  drill. 
Another  test  showed  1.21  in.  per  minute  for  Konomax  drill  at  50 
Ib.,  and  at  55  Ib.  pressure,  1.48  in.  per  minute. 

In  June,  1908,  in  the  Journal  of  the  South  African  Associa- 
tion of  Engineers,  Mr.  E.  J.  Laschinger  gives  results  of  a  com- 
parative working  test  lasting  15  days.  The  drills  used  were  the 
new  Konomax  3j-in.  drills,  new  Ingersoll  3J-in.  drill,  and  old 
Ingersoll  3J-in.  drills,  some  of  which  had  been  at  work  for  four 
years,  but  which  had  been  recently  thoroughly  overhauled.  This 
was  designed  as  a  practical  test  under  working  conditions.  Many 
exact  determinations  were  made.  The  accompanying  Table  V 
shows  some  of  the  data  obtained.  (See  table  on  next  page.) 

Some  of  the  principal  results  are  as  follows : , 

(1)  At  65.3  Ib.  surface  pressure,  when  drilling  the  same  aver- 
age depth  of  hole  (63 £  in.)  and  about  the  same  percentage  (average 
8^)  of  dry  hole,  the  Konomax  drill  used  24.4  per  cent,  less  air  per 
inch  drilled  than  the  new  Ingersoll.     During  this  test  the  Konomax 
drilled  on  the  average  3.6  per  cent,  faster  than  the  Ingersoll. 

(2)  At  74.4  Ib.  surface  pressure,  when  drilling  the  same  aver- 
age depth  of  hole  (63 £  in.),  and  about  the  same  percentage  depth 
of  dry  hole  (8.1  per  cent.),  the  Konomax  used  about  5.1  per  cent. 


330 


ROCK   DRILLS 


TABLE  V.     ROCK  DRILL  TESTS  —  MEYER  AND  CHARLTON  —  MAY,  1908 

PRINCIPAL   DATA-  AND  RESULTS.       AVERAGES    PER   DRILL    SHIFT 


New 
Ingersolls 
A 

New 
Konomax 
B 

New 
Konomax 
C 

Old 
Ingersolls 
D 

Old 
Ingersolls 
E 

1.  Revs,    of    compressor 

• 

chargeable  

658.36 

548.10 

582.39 

1021.29 

1002.00 

2.  I.  H.  P.    hours    steam 

cylinders  

41.924 

34.879 

39.428 

72.261 

65.991 

3.  I.H.P.   hours  air  cylin- 

ders   

38.769 

32.204 

36.898 

66.268 

60.595 

4.  Mechanical  efficiency  of 

compressor,  per  cent.  .  .  . 

92.47 

92.33 

93.58 

91.71 

91.8 

5    Free  air  cubic  ft. 

19638.9 

15360.0 

17372.7 

30465.1 

20889.6 

6.  Inlet  press,  of  air,  bar.  in. 

24.780 

24.828 

24.722 

24.666 

24.660 

7.  Inlet  press,  of  air,  Ib.  sq. 

in  

12.17 

12.19 

12.14 

12.11 

12.11 

8.  Inlet  temperature  of  air, 

deg   Fah 

83.96 

85.58 

76.60 

80.40 

81.51 

9.  Weight  of  air  delivered, 

Ib.        .              

1187.2 

987.3 

1062.0 

1845.2 

1806.2 

10.  Press,  at  receiver,  Ib.  sq. 

in  

65.30 

65.30 

74.39 

73.16 

64.20 

11.  Press,  at   llth   Station, 

Ib.  sq.  in. 

65.21 

65.70 

75.61 

72.41 

61.68 

12.  Temp,  at    llth  station, 

deg.  Fah  

68.57 

65.29 

64.13 

69.89 

67.33 

13.  Depth  drilled,  in  

301.87 

332.47 

335.95       . 

286.48 

287.15 

14.  No.  of  holes  

4.7591 

5.2042 

5.3043 

4.5417 

4.6250 

16.  Average  depth  of  hole, 

• 

in  

63.43 

63.88 

63.33 

63.08 

62.19 

16.  Ratio  depth  dry  holes  to 

total,  per  cent  

8.16 

9.04 

7.12 

12.36 

11.23 

17.  Drilling  time  l  hrs.  and 

min.    . 

6  —  15 

6  —  42 

6  —  23 

g  17 

g  44 

18.  Revs,  of  compressor  per 

inch  drilled    

2.1809 

1.6486 

1.7335 

3.5650 

3.4834 

19.  Steam  H.  P.  hours  per 

inch  drilled    

0.13888 

0.10491 

0.11736 

0.25244 

0.22942 

20.  Air  H.  P.  hours  per  inch 

drilled  

0.12843 

0.09686 

0.10983 

0.23131 

0.21066 

21.  Free  air  per  inch  drilled, 

cu.  ft. 

65.057 

49.178 

51.711 

106.343 

104  090 

22.  Lbs.  air  per  inch  drilled  . 

3.9329 

2.9697 

3.1612 

6.4408 

6.2901 

23.  Rate    of    drilling    over 

total    drilling    time    of 

shift,   in.    min. 

0.8050 

0.8270 

0.8771 

0  7599 

0  7108 

24.  Relative    rev.    of    com- 

pressor per  inch  drilled  .  . 

100 

75.59 

79.49 

163.46 

159.72 

25.  Rel.   steam   power   con- 

sumption of  drills  

100 

75.53 

84.50 

181.62 

165.47 

26.  Rel.  air  power  consump- 

tion of  drills 

100 

75.42 

85.51 

180.10 

164.02 

1  This  refers  to  the  time  interval  from  commencement  of  first  hole  to  finish  of  last  hole. 
Average  temperature  of  air  in  mine  68°  F. 


ROCK  DRILL  TESTS  AND  CONTESTS  331 

more  air  per  inch  drilled,  while  drilling  about  6  per  cent,  faster 
than  the  same  drills  at  65.3  Ib.  pressure. 

(3)  The  renovated  old  Ingersoll  drills,  at  64.2  Ib.  surface  pres- 
sure, used  59.7  per  cent,  more  air  per  inch  drilled  than  the  new 
Ingersoll  at  65.3  Ib.  pressure,  while  the  drilling  speed  dropped  off. 
11  per  cent. 

(4)  The  renovated  old  Ingersolls,  at  73.16  Ib.  pressure,  used 
2.3  per  cent,  more  air  per  inch  drilled  than  when  working  at  64.2 
Ib.  pressure  and  drilled  6.8  per  cent,  faster. 

(5)  From  figures  supplied  by  the  manager  of  the  Meyer  & 
Charlton  (Mr.  Nitch),  as  to  the  revolutions  of  the  compressor  for 
five  weeks  previous  to  the   test,   when   the  old  Ingersolls  were 
working  (before  they  were  thoroughly  overhauled  in  the  shops), 
it  appears  that  the  old  Ingersolls  then  consumed  about  12  per 
cent,  more  air  than  after   they  were  renovated.     The   footage 
drilled  then  was  not  measured,  but  was  considerably  less  than 
during  the  test  on  the  27th  May. 

Comparing  this  record  with  new  Ingersoll  gives  the  result 
that  the  old  machines  then  used  over  80  per  cent,  more  air  per 
inch  drilled  than  new  machines. 

(6)  A  dry  hole  took  on  the  average  55.6  per  cent,  more  time  to 
drill  than  a  wet  hole,  depth  of  holes  5  ft.     (This  is  on  the  basis  of 
total  time  from  start  to  finish  of  holes,  including  change  of  bits.) 

(7)  It  is  worthy  of  notice  that,  although  the  white  men  and 
natives  drilling  were  unaccustomed  to  the  use  of  the  Konomax, 
they  found  no  difficulty  in  handling  it,  and  the  work  even  on  the 
first  day  was  fully  up  to  the  standard. 

(8)  It  is  also  to  be  noted  that  the  average  depth  of  hole  dur- 
ing these  tests  was  only  about  5  ft.  3  in.     The  deepest  holes  drilled 
were  about  6  ft. 

These  results  would  have  been  more  interesting  if  old  Konomax 
drills  had  also  been  available,  and  if  it  had  been  possible  to  get 
some  idea  of  the  number  of  .cubic  inches  drilled  for  a  comparison 
with  other  tests  regarding  air  consumption.  The  air  consumption 
for  linear  inch  drilled  is  naturally  smaller  than  that  shown  in  other 
tests,  owing  to  the  smaller  average  diameter  of  bits  employed. 

STOPE  DRILL  TESTS 

In  December,  1907,  a  series  of  trials  of  small  stoping  machines 
was  carried  out  by  the  proprietor  of  the  South  African  Mining 


332 


ROCK   DRILLS 


Journal  in  Johannesburg.  This  was  supervised  by  Professor  J. 
Orr.  A  number  of  most  exact  determinations  of  boring  speed  in 
wet  and  dry  holes  with  bits  of  various  diameters  were  made. 
The  accompanying  Table  VI  shows  the  machines  used: 

TABLE  VI.     THE  MACHINES  TESTED 


Name  of  Drill 

Type 

Diameter  Cylinder  and  Valve 

Length 
Stroke 

Weight 
Hammer 

Hammer 

31-in.  Valveless 

3" 

12  Ibs. 

Little  Wonder    

Piston 

2-in.  Tappet  valve,  hollow  steel 

5" 

Gordon  

Hammer 

116-in.  Spool  valve,  hollow  steel 

•      10" 

IJlb. 

Little  Kid  

Piston 

2-in.  Little  Giant,  tappet  valve 

5" 

— 

Baby  Ingersoll   

Piston 

2J-in.  Arc  valve,  tappet 

5" 

— 

Flottman     

Hammer 

2-in.  Ball  valve 

3" 

3  Ibs. 

Little  Holman    

Piston 

2-in.  Auxiliary  valve  and  spool  valve 

5" 

— 

Chersen     

Piston 

2f-m.  Vale  valve 

6" 



This  test  was  most  carefully  carried  out,  the  machines  boring 
for  four  hours  on  the  surface  and  sixteen  hours  underground.  The 
winning  drill,  however,  proved  an  utter  failure  in  actual  practice. 

Drilling  Speed  and  Air  Practice.  —  The  increase  of  drilling 
speed  in  relation  to  air  pressure  is  shown  in  accompanying  Table 
VII.  Relative  air  consumption  and  number  of  blows  struck 
per  minute  were  not  exactly  determined.  The  air  consumption 
of  the  2-in.  Holman  drill  has  since  been  determined  at  60  Ib. 
pressure  to  be  30  cu.  ft.  of  free  air  per  minute. 


TABLE  VII. 


SHOWING  INCREASE  OF  DRILLING  SPEED  WITH  INCREASE 
OF  PRESSURE 


Name  of  Drill 

Depth  Drilled  at 
50  Ibs.  Air  Pressure 

Depth  Drilled  at 
60  Ibs.  Air  Pressure 

Percentage  Increase 
in  Depth  Dr'lled  at 
60  Lbs.  Pressure 

Kimber  .  .  . 

12'  llf" 
16'  7f" 

28'  4f" 

15'  9f* 
25'  3" 
18'  19f 
14'  41' 
26'  5f    ' 

16'  11" 

19'  llf" 
36'  91' 
22'  6i" 
29'  6^" 
25'  4|» 

17'  or 

33'  2" 

30.6% 
19.7% 

29.5% 
42.6% 
17% 
34.4% 
18.6% 
26.0% 

Little  Wonder    .  .  . 

Gordon    .  . 

Little  Kid  .  .  . 

Baby  Ingersoll  
Flottmann    
Little  Holman     .  . 

Chersen     

Mean  percentage  increase  . 


27.3% 


ROCK   DRILL  TESTS   AND   CONTESTS 


333 


The  thorough  manner  in  which  results  were  recorded  in  the 
surface  trials  is  shown  in  Table  VIII  on  page  336. 

TRANSVAAL  STOPE  DRILL  COMPETITION 

The  accompanying  table  gives  some  results  of  the  Transvaal 
stope-drill  competition  with  simple  averages  of  distances  drilled 
and  air  consumption  worked  out.  The  pressures  used  were  not 
uniform  up  to  September,  but  during  that  month  they  were  most 
closely  regulated,  varying  from  69.1  Ib.  per  sq.  in.  on  the  Siskol 
to  60.1  on  the  Holman. 

CHERSEN 


Inches  per 
Minute 

Elimination 4.110 

June  17-22 3.27 

July  26 3.74 

August  19-31 2.16 

September  21-29 3.523 

Average 3.36 

SISKOL 

Elimination 4.46 

June  17-22 2.59 

July  21 3.00 

July  26 2.85 

August  19-31 3.21 

September  21-29 4.00 

Average 3.35 

HOLMAN  2|-iNCH 

Elimination 3.12 

June  17-22 2.47 

July  21-22 3.75 

August  19-31 2.898 

September  21-29 2.55 

Average 2.957 

CLIMAX  IMPERIAL 

Elimination 3.52 

June  17-22 3.03 

July  21 2.55 

July  26 3.04 

August  19-31 , 2.44 

September  21-29 2.52 

Average 2.85 


Free  Air 

per  Foot 

Drilled 

239.9 
310.4 
252.0 
256.6 
281.9 

268.1 


202.4 

362.5 

321.2 

397.4 

317.66 

216.2 

302.89 


385.14 

646.3 

346.0 

325.6 

445.4 

429.688 


329.74 


334  ROCK  DRILLS 

NEW  CENTURY  00 
Elimination  2.33  276.6 


June  17-22 2-19 


358.8 

July21-26 2.13  351'7 

AugustKHil 2.77  253.3 

September  21-29  • 2.70  330.6 


Average 2.424  314.2 

HOLMAN    2J-INCH 

Elimination 2.40  376.2 

Junel7-22 1-85  452.5 

July  21-26 2.38  397'5 

Augustl9-31 2.33  285.5 

September  21-29 2.45  368.0 

Average 2.282  375.94 

The  distance  drilled  is  about  the  same  for  the  Chersen  and 
the  Siskol,  but  the  air  consumption  of  the  former  was  only  268 
against  303.  These  are  the  only  two  drills  which  cut  more  than 
three  inches  per  minute. 

MISCELLANEOUS  DRILL  TESTS 

Accounts  of  numerous  so-called  contests  between  drills  have 
also  been  published  as  taking  place  in  various  mines  and  at 
exhibitions.  Generally,  no  exact  data  have  been  furnished  with 
these  accounts,  and  as,  especially  with  hammer  drills,  many  types 
manufactured  have  since  been  improved,  it  is  scarcely  right  to 
give  comparative  results  which  might  be  unfair  to  manufacturers 
and  misleading  to  users. 

GENERAL  REMARKS  ON  DRILL  TESTS 

It  will  be  seen  from  the  foregoing  records  that  the  carrying  out 
of  a  really  authoritative  comparative  test  of  the  relative  air  con- 
sumption, boring  speed,  and  ease  of  manipulation  of  a  number 
of  machines  would  be  a  most  formidable  task.  Both  old  and 
new  machines  would  have  to  be  tested.  The  test  would  have  to 
be  somewhat  of  a  combination  of  Mr.  Holloran's  investigations, 
the  use  of  Messrs.  Goffe  &  Company's  air  consumption  recording 
device,  the  accurate  timing  of  Professor  Orr  in  some  surface 
trials,  boring  holes  in  various  directions  to  some  depth,  and  a 
comprehensive  underground  test  such  as  Mr.  Laschinger  carried 
out  on  the  Meyer  &  Charlton  mine. 

Future  Development  of  Rock  Drills.  —  It  is  difficult  to  suggest 


ROCK  DRILL  TESTS  AND  CONTESTS  335 

with  confidence  the  lines  along  which  rock-drilling  machines  will 
be  developed.  Points  to  be  aimed  at  have  been  shown  to  be: 
(a)  The  rapid  removal  of  rock  fragments  from  the  end  of  the 
hole  and  from  the  front  of  the  cutting  bit;  (6)  Maximum  out- 
put of  energy  per  unit  weight;  (c)  Strength,  simplicity,  and 
resistance  to  wear;  (d)  Easy  replacement  of  worn  parts;  (e) 
Mechanical  efficiency.  The  hammer  drill,  owing  to  its  numerous 
advantages  for  certain  work,  seems  to  be  encroaching  on  the 
sphere  of  the  piston  drill.  It  has  already  largely  replaced  small 
piston  drills  for  most  work,  and  new  models  are  constantly  appear- 
ing, claiming  to  eliminate  drawbacks  and  defects.  Though  piston 
drills  hold  their  own  for  long  deep  holes  of  large  diameter,  in  hard 
ground,  yet  the  Leyner  hammer  drill  is  in  some  places  doing  the 
same  work.  Conditions  vary  so  greatly  that  nearly  all  the  types 
of  drills  mentioned  have  their  place  and  may  do  better  work  in 
that  place  than  others.  It  seen.s  to  me  that  the  ideal  piston 
drill  of  the  future  might  be  constructed  to  work  on  a  short  stroke 
with  water  injection  or  air  and  water  injection.  The  piston 
would  be  single  headed,  short,  and  wear  on  the  cylinder  would 
be  provided  for  by  liners  easily  replaced. 

Direct  and  rapid  air  admission  and  exhaust  would  be  arranged 
for  either  on  the  Konomax  principle  or  by  two  light  Corliss  valves 
like  those  used  in  the  Baby  Torpedo  drill,  but  operated  by  air 
or  auxiliary  valves.  Such  a  machine  would  tend  to  combine 
the  advantage  of  both  piston  and  hammer  drills. 

The  hammer  drill  evolved  on  the  lines  of  the  latest  models, 
and  with  improved  materials  used  in  its  construction,  must 
increase  its  range  of  usefulness.  With  air  pressure  of  100  Ib.  ordi- 
nary steel  snaps  off  about  4  in.  from  the  shank  owing  to  some 
peculiar  fatigue  due  to  the  blows  and  vibration.  "  At  the  present 
time  the  capacity  (power)  is  limited  by  the  ability  of  the  drill  steel 
to  withstand  the  blows  of  the  hammer."  The  electric-air  drill 
has  come  to  stay  for  certain  work.  The  electric  drill  proper  will 
find  certain  limited  spheres  of  usefulness.  An  electric-rotary  drill 
may  be  further  developed  to  bore  rock  somewhat  harder  than  it 
can  attack  at  present.  The  manager  will  do  well  to  allow  some- 
body else  to  prove  any  new  drill  submitted  to  him  no  matter  how 
attractive  its  general  design  may  be.  Minor  troubles  are  sure  to 
show  themselves  if  greater  ones  do  not,  and  it  is  not  wise  to  dis- 
card old  and  tried  friends  until  better  ones  have  proved  themselves. 


336 


ROCK   DRILLS 


TABLE  VIII.     SOUTH  AFRICAN 

GENERAL    SUMMARY   OF    SUR 
Trials  No.  1  at  50  Ib.  and  Trials  No.  2  at  60 


Kimber 
No.  1 

Kimber 
No.  2 

Little 
Wonder 
No.  1 

Little 
Wonder 
No.  2 

Gordon 
No.  1. 

Gordon 
No.  2 

1st  Hole 

Mean  time  to  start  drilling  after  sig- 

nal                                                

8m.  4.7s. 

5m.  25s. 

5m.  27s. 

7m.  40.7s. 

1m.  31s. 

1m.  43s. 

Mean  diameter  of  first  steel    

U" 

11" 

1!" 

if 

U" 

H" 

Mean  depth  drilled  with  first  steel.  . 

6.4" 

10" 

8.9" 

6.7" 

6  9-16" 

5  15-16" 

Mean  time  of  drilling  with  first  steel  . 

7m.  18.2s. 

8m.  8s. 

8m.   58s. 

9m.  54s. 

4m.  46fs. 

3m.  3s. 

Mean  time  elapsing  between  stopping 

and  re-starting  in  changing  steels. 

1m.  4.2s. 

58s. 

44.5s. 

42.5s. 

14.5s. 

14.7s. 

Mean  diameter  of  second  steel  

1|" 

If" 

n" 

H" 

H" 

11" 

Mean  depth  drilled  with  second  steel. 

6.0" 

5  3-16" 

13.1" 

m* 

81" 

8  15-16" 

Mean  time   of  drilling  with   second 

steel  

5m.   36s. 

4m.  12s. 

— 

12m.  2s. 

6m.  14s. 

4m.  30s. 

Mean  time  elapsing  between  stopping 

and  re-starting  in  changing  steels  . 

2m.  8.2s. 

1m.  34s. 

51.2s. 

50.5s. 

29  Js. 

18.5s. 

Alean  diameter  of  third  steel 

If" 

If" 

U" 

U" 

U" 

U" 

Mean  depth  of  drilling  with  third  steel 

5.7" 

8|" 

12.6" 

9f" 

lOi" 

10  5-16" 

Mean  time  of  drilling  with  third  steel 

7m.  31.2s. 

5m.  7s. 

7m.  38.7s. 

5m.  15s. 

6m.  18fs. 

4m.  24s. 

Mean  time  elapsing  between  stopping 

and  re-starting  in  changing  steels. 

1m.  52.2s. 

1m.  42s. 

46.7s. 

1m.  16s. 

26  fs. 

26.7s. 

Mean  diameter  of  fourth  steel  

n" 

H" 

U" 

H" 

H" 

U" 

Mean  depth  drilled  with  fourth  steel  . 

6.4" 

61" 

8.4" 

11.6" 

14  f" 

155" 

Mean  time  of    drilling   with  fourth 

steel  

5m.  52.7a. 

2m.  58s. 

5m.  2s. 

3m.  51s. 

7m.  32Js. 

6m.  10.7s. 

Mean  time  elapsing  between  stopping 

and  re-starting  in  changing  steels. 

2m.  43.5s. 

2m.  52s. 

— 

— 

— 

— 

Mean  diameter  of  fifth  steel  

1!" 

1|* 







— 

Mean  depth  drilled  with  fifth  steel  .  . 

7.1" 

lit* 

— 

— 

— 

— 

Mean  time  of  drilling  with  fifth  steel  . 

6m.  42s. 

4m.  49s. 

— 

— 

— 

— 

Mean  time  elapsing  between  stopping 

and  re-starting  in  changing  steels. 

2m.  42s. 

— 

— 

— 

— 

— 

Mean  diameter  of  sixth  steel  

U* 

— 







— 

Mean  depth  drilled  with  sixth  steel  .  . 

5.3" 

— 

— 

— 

— 

— 

Mean  time  of  drilling  with  sixth  steel 

3m.  36s. 

— 

— 

— 

— 

— 

Mean  time  elapsing  between  stopping 

and  re-starting  in  changing  steels  . 

2m.  18s. 

— 

— 

— 

— 

— 

Mean  diameter  of  seventh  steel  

H" 

— 

— 

— 

— 

— 

Mean  depth  drilled  with  seventh  steel 

5f" 

— 

— 

— 

— 

— 

Mean  time  of  drilling  with  seventh 

* 

steel 

2m.  57s. 

~ 

~ 

~ 

~ 

~ 

ROCK   DRILL  TESTS  AND  CONTESTS 


337 


MINES  STOPE   DRILL   COMPETITION 
FACE  TRIALS,  BY  PROF.  J.  ORR 

lb.  Air  Pressure  per  Square  Inch,  respectively 


Little 
Holman 
No.  1 

Little 
Holman 
No.  2 

Chersen 
No.  1 

Chersen 
No.  2 

Little 
Kid 
No.  1 

Little 
Kid 
No.  2 

Baby 
Inger- 
soll 
No.  1 

Baby 

Inger- 
soll 
No.  2 

Flott- 

mann 
No.  1 

Flott- 
mann 
No.  2 

4m.  44s. 

3m.  9s. 

3m.  45s. 

2m.  56s. 

4m.  18s. 

3m.  51s. 

4m.    2s. 

3m.  28s. 

3m.l3s. 

4m.  59s. 

If 

If 

II* 

1  21-32" 

II* 

H* 

11* 

U" 

H" 

a* 

91" 

7  9-16" 

10|" 

5  11-16" 

10f" 

8|* 

111" 

8" 

4  9-16" 

4f* 

llm.  48s. 

8m.  18s. 

7m.38s. 

4m.  8s. 

13m.  38s. 

6m.  23s. 

8m.  24s. 

4m.  42s. 

6m.  16s. 

4m.  47s. 

42s. 

27s. 

30s. 

27s. 

39s. 

57s. 

40s. 

33s. 

17s. 

12s. 

H* 

If" 

If 

1  9-16" 

If" 

If" 

If" 



1  1-76" 

1  7-16" 

7   9-16" 

9" 

101" 

10" 

10J" 

8}" 

9|" 

8  5-16" 

45-16" 

6  3-16" 

10m.43s. 

8m.  58s. 

7m.  35s. 

4m.  20s. 

9m.  46s. 

6m.  17s. 

6m.  54s. 

3m.  44s. 

2m.32s. 

3m.  23s. 

44s. 

47s. 

55s. 

44s. 

1m.  15s. 

55s. 

1m.  6s. 

51s. 

29s. 

15s. 

11* 

H" 

u« 

U" 

n" 

n" 

U" 

— 

If" 

If" 

101" 

lot" 

13  i" 

10  5-16" 

7  3-16" 

10J" 

8" 

8" 

51" 

5  1-16" 

12m.  11s 

6m.  58s. 

9m.  32s. 

4m.    40s. 

9m.  56s. 

7m.  29s. 

6m.  21s. 

4m.  14s. 

2m.52s. 

4m.  8s. 

56s. 

39s. 

49s. 

45s. 

2m.  9s. 

1m. 

1m.  20s. 

1m.  26s. 

1m.  2s. 

1m.  57s. 

i|* 

— 

U" 

1  3-16" 

11* 

14* 

!i* 

— 

H" 

H" 

iof" 

10i" 

8f" 

10|" 

12f" 

113  16 

10|* 

101" 

101" 

13" 

5m.  47s. 

7m.  15s. 

2m.  32s. 

4m.  S8s. 

7m.  Is. 

7m.  45s. 

6m.  25s. 

8m.  58s. 

5m.27s. 

5m.  11s. 



53s. 



59s. 







1m.  30s. 

33s. 

33s. 

— 

— 

— 

1   7-16" 

— 

— 

— 

— 

U" 

H" 

— 

4|" 

— 

7," 

— 

— 

— 

3" 

51" 

91-16" 

— 

10m.23s 

— 

10m.  23s. 

— 

— 

— 

6m.  37s. 

4m.43s. 

5m.  17s. 



47s. 

— 

1m.  37s. 

— 

— 









— 

— 

— 

U" 

— 

— 

— 

— 

— 

— 

— 

2" 

— 

5" 

— 

— 

— 

— 





— 

2m.  20s. 

— 

10m.  55s. 

— 

— 

— 

— 

— 

— 

XV 
DUST  AND  ITS  PREVENTION 

IT  was  early  recognized  that  one  of  the  main  essentials  for 
rapid  drilling  was  the  immediate  removal  of  the  rock  as  broken 
from  the  bottom  of  the  hole.  This  could  best  be  done  by  direct- 
ing a  jet  of  air  or  water  into  the  bottom  of  the  hole  while  drilling 
goes  on.  This  can  be  done  in  two  ways:  either  a  hollow  boring 
tool  can  be  used  and  the  air,  water,  or  both  can  be  passed  through 
it  to  the  cutting  edge;  or,  a  jet  of  water  or  air  under  pressure 
may  be  passed  down  between  the  sides  of  the  hole  and  the  drill 
shank. 

Air  alone  used  in  either  manner  is  not  perfectly  satisfactory. 
It  prevents  water  reaching  the  bottom  of  the  hole;  the  drill  bit 
is  not  kept  sufficiently  cool,  and  tends  to  lose  its  temper;  dust 
is  produced  in  large  quantities.  While  an  upper  hole  can  be 
bored  very  much  more  rapidly  with  hollow  steel  and  air,  yet  in 
most  down-holes  the  difference  in  boring  speed  is  not  marked. 

Water  Jets.  —  These  are  effective  means  of  clearing  holes 
down  to  a  certain  depth;  the  limiting  depth  for  up-holes  being 
about  4  ft.  Water  may  be  supplied  under  natural  or  artificial 
pressure.  For  producing  artificial  pressure  tanks  such  as  that 
shown  in  the  illustration  of  No.  3  Murphy  drill  may  be  employed, 
the  pressure  being  given  by  the  compressed  air  acting  on  the 
surface  of  the  water,  Fig.  186. 

The  jet  is  employed  by  connecting  2  to  4  ft.  of  s-in.  or  f-in. 
pipe  to  the  hose  supplying  water  under  pressure.  The  pipe  is 
fitted  with  a  tV  or  i-in.  nozzle.  With  a  large  down-hole  the  pipe 
may  be  lowered  into  the  hole  as  drilling  proceeds.  With  other 
holes  the  jet  must  be  directed  as  well  as  possible  up  the  hole. 
For  driving  levels  in  the  North  of  England  coal  mines,  Professor 
Galloway  designed  a  special  carriage  containing  a  tank  with  water 
under  pressure.  This  served  to  supply  water  for  jets  and  also 
for  fixing  a  horizontal  bar  across  the  level  by  means  of  hydraulic 
rams.  On  the  bar  were  mounted  two  rock  drills.  Holes  were 

338 


DUST  AND  ITS  PREVENTION 


339 


bored  4  ft.  long  and  the  drive  was  advanced  very  rapidly,  the 
only  delay  being  caused  by  firing  and  removing  all  broken  rock 
before  drilling  could  be  resumed.  Miners  as  a  rule  dislike  jets  and 
refuse  to  use  them.  They  must  be  held  in  the  hand  and  it  is 
hard  to  keep  them  directed  exactly  into  the  hole  or  parallel  with 
the  hole;  hence,  there  is  much  water  sprayed  about,  rendering 
work  uncomfortable. 

Mr.  H.  P.  Stow  quotes  an  experiment  in  which  the  use  of  jets 
increased  the  feet  bored  per  shift  by  11  per  cent.,  using  fewer 
drill  bits.  When  an  attempt  is  made  to  send  a  jet  up  an  upper 
or  dry  hole  more  than  3  or  4  ft.  deep,  stiff  mud  is  formed  in  the 
hole,  the  drill  sticks  and  often  cannot  be  withdrawn.  However, 

Compressed  <*t-r 

in  Let  Water  outLet 


FIG.  186.  —  Tank  for  Murphy  drill. 

under  certain  circumstances,  with  miners  who  will  take  the  trouble 
to  use  them,  jets  increase  boring  speed  and  prevent  dust. 

Effect  of  Dust  Produced  in  Rock  Drilling.  —  The  particles  of 
broken  rock  produced  by  drilling  up-holes,  without  water,  have 
a  deadly  effect  on  those  constantly  inhaling  it.  The  particles 
are  retained  in  the  tissues  of  the  lungs,  gradually  choking  them 
up,  which  renders  the  tissue  susceptible  to  phthisis  and  pneu- 
monia. This  action,  combined  with  the  effect  of  gases  due  to 
imperfect  combustion  of  explosives,  renders  rock  drilling,  espe- 
cially in  some  fields,  one  of  the  most  dangerous  occupations.  It 
has  been  stated  that  the  average  life  of  a  rock  drill  operator  on 
the  Witwatersrand  is  about  five  years.  There  is  thus  a  humani- 
tarian reason,  as  well  as  an  economic  reason,  for  the  prevention 
of  the  formation  of  dust  in  bore  holes,  or  for  allaying  it  after 
production. 


340 


ROCK   DRILLS 


Respirators.  —  Respirators  can  be  used  to  prevent  dust  reach- 
ing the  lungs,  but  they  cannot  be  worn  continuously,  as  it 
is  impossible  to  do  heavy  muscular  work  while  wearing  them. 
In  certain  cases  they  are  useful,  especially  where  men  use  air- 
feed  hammer  drills  in  stoping  and  have  merely  to  stand  and 
reciprocate  them  while  they  are  boring. 

Masks  have  been  tried,  supplied  by  a  small  hose  with  com- 
pressed air.  These  are  much  more  pleasant  to  use;  but  com- 
pressed air  contains  sometimes  poisonous  carbon  monoxide  from 


FIG.  188.  —  The  Holman  spray. 

the  compressor  lubrication;  tubes  hamper  work  and  are  in  the 
way  in  confined  spaces  underground. 

Numerous  dust  collectors  have  been  invented,  but  none  of 
them  are  practical  devices. 

Sprays.  —  Several  sprays  using  a  mixture  of  compressed  air 
and  water  are  on  the  market.  The  Holman  spray  is  shown  in 
the  accompanying  section,  Fig.  188.  The  Climax  spray  is  shown  in 
Fig.  189,  attached  to  drill.  It  is  of  somewhat  similar  design. 
There  are  several  other  patterns  and  a  device  can  easily  be  made 
at  a  mine  for  attachment  to  the  valve  chest  of  drill.  With  care- 
ful workmen,  sprays  are  advantageous;  they  settle  about  75  per 
cent,  of  the  dust  produced. 

Objections  to  Sprays.  — They  are  not  favorites  with  most  miners 


DUST  AND   ITS   PREVENTION  341 

and  as  a  result  they  neglect  to  use  them.  With  unskilled  labor 
handling  drills  they  are  liable  to  damage.  They  produce  a  damp- 
ness which  miners  complain  tends  to  rheumatism.  Clean  and 
wholesome  water  is  not  always  procurable  underground,  and  more 
damage  to  health  might  be  done  by  inhaling  a  spray  of  disease- 
laden  water  than  by  inhaling  the  dust.  Water  often  contains 


FIG.  189.  —  Stephens  patent  " Climax"  dust  allayer  in  use. 

grit,  which  is  liable  to  choke  the  small  tubes  and  narrow  parts  of 
the  spray.  The  miner  is  generally  more  concerned  about  making 
money  than  about  his  health,  and  unless  compelled  by  law  will 
generally  use  none  of  these  devices  because  they  are  complicated. 
In  a  mine  of  which  I  was  manager  I  provided  water  in  pipes  under 
moderate  pressures  to  every  working  face,  with  sprays  or  jets. 
They  were  never  used.  I  also  provided  a  variation  of  James's 


342  ROCK  DRILLS 

water  blast,  Fig.  190,  by  using  about  3  ft.  of  1-in.  pipe  with  T- 
piece  with  spuds  fitted  to  one  end.  Just  before  blasting,  the  air- 
hose  union  was  attached  to  the  one  on  the  end  and  the  union 
on  the  water  hose  to  the  other.  These  were  both  turned  on  and 


/'  Ptpe  _ 

=*  -*  Spray 


FIG.  190.  —  Variation  of  James's  water  blast. 

the  pipe  placed  at  a  convenient  distance  back  from  the  face, 
pointing  in  such  a  direction  as  to  allow  the  cloud  of  spray  formed 
to  meet  and  absorb  the  gases  from  the  explosion,  cooling  the  air 
and  rock. 

MACHINES  AND  DEVICES  FOR  USING  HOLLOW-DRILL  STEEL 

Piston  Drills.  —  One  of  the  earliest  devices  for  using  water 
and  hollow  steel  is  shown  in  an  old  German  patent,  Fig.  191.  It 
is  practically  the  same  as  that  shown  in  drawing  of  the  Box 
hammer  drill.  Bolted  to  the  body  of  drill  D  was  a  bracket  carry- 
ing a  hollow  cylinder  with  a  water  space  in  the  middle  with  packing 
glands  at  each  end.  A  small  transverse  hole  in  drill  connected 


Water  space.  ^])rLLL  steel 


FIG.  191.  —  An  old  German  device  for  preventing  dust. 

the  hollow  core  to  the  water  space,  and  the  drill  was  supposed  to 
revolve  and  reciprocate  through  the  cylinder  which  fed  water. 

This  device  applied  to  a  piston  drill  was  utterly  impracticable. 
Packing  could  not  be  kept  tight  while  allowing  the  machine  a  free 
stroke,  and  the  drill  was  weakened  by  boring  a  lateral  hole  in  it. 

The,  Bornet  System.  —  "With  this  system  there  is  an  inter- 
mittent discharge  of  water  at  the  point  of  the  borer,  the  bit 
being  hollow,  as  seen  at  Fig.  192.  A  supply  of  water  is  held  in  a 


DUST  AND  ITS   PREVENTION  343 

cistern  and  fed  under  pressure  to  the  front  head  of  a  standard 
percussive  air  drill  by  means  of  flexible  hose.  Here  the  water 
passes  through  a  valve  into  a  water  chamber  arranged  in  the 
front  cover  piston  bearings.  The  hollow  borer  bit  is  fastened  in 
the  drill  chuck,  which  is  provided  with  a  stuffing-box  to  prevent 
leakage,  and  the  piston  for  some  distance  back  from  the  chuck 
is  hollowed  out  longitudinally,  and  then  diagonally.  At  each 
stroke  of  the  piston  this  diagonal  hole  passes  the  water  chamber, 
and  in  so  doing  takes  a  supply  of  pressure  water  which  travels 
through  the  hollow  piston  and  onwards  through  the  borer,  finally 
being  ejected  at  the  drill  point.  By  the  arrangement  of  the 
diagonal  passage,  and  owing  to  the  water  chamber  being  con- 
siderably shorter  than  the  stroke  of  the  machine,  the  jet  is  only 
projected  just  before  and  after  the  cutting  stroke.  All  dust  is 
effectually  killed,  the  drill  point  kept  cool  and  the  bottom  of  the 


FIG.  192.  —  Bornet  hollow  drill  bit  for  allaying  dust. 

hole  maintained  clear  of  all  chips  which  are  forced  from  the  hole 
by  the  pressure  water.  The  jet  being  intermittent,  only  a  small 
quantity  of  water  is  used,  about  14  gallons  sufficing  for  a  shift." 
This  appears  at  first  sight  to  afford  a  satisfactory  solution  of 
the  problem.  Practical  difficulties,  however,  at  once  present 
themselves.  In  the  first  place  the  end  of  the  shank  tends  to  burr 
up  and  close  the  hole  in  the  bottom  of  the  chuck.  It  is  hard  to 
keep  a  tight  contact  here  also,  as  any  packing  tends  to  be  dis- 
placed or  ground  up.  Wear  occurs  on  the  piston  and  front 
head.  The  water  leaks  out  of  the  front  end,  and  works  back- 
ward into  the  cylinder.  Another  trouble  becomes  apparent  in 
practice.  If  the  water  is  not  turned  on  and  issuing  from  the 
hole  in  the  drill  bit  in  sufficient  quantity  before  cutting  rock  be- 
gins, a  stiff  mud  is  formed,  which  is  forced  into  the  central  core  and 
stops  it  up.  This  is  a  great  trouble  with  any  water-feed  device 
that  is  not  automatically  turned  on  when  the  machine  starts. 


344  ROCK  DRILLS 

Derby  Tubular  Bit.  —  The  Derby  tubular  bit  was  used  for 
several  months  in  drilling  flood  rock.  H.  P.  Gillette  writes: 

"  Major  Geo.  McC.  Derby  invented  a  drill  bit  that  was  used 
in  drilling  on  the  flood  rock  work,  and  it  proved  so  greatly  su- 
perior to  the  cross-bits  that  I  regard  it  as  worthy  of  special 
description.  Major  Derby  writes  me  that  he  patented  the  drill  bit 
in  1885  and  sold  the  patent  rights  to  the  Rand  Drill  Company, 
which,  for  reasons  unknown  to  him,  has  never  placed  it  upon  the 
market.  The  drill  steel  was  hollow,  as  was  also  the  bit  which  was 
provided  with  six  points  or  teeth.  The  bits  were  sharpened  very 
much  like  the  bits  used  in  the  plug  drills  made  by  the  C.  H.  Shaw 
Pneumatic  Tool  Company,  of  Denver,  Colorado.  Each  bit  was 
only  2  to  6  in.  long  and  fastened  to  the  end  of  the  hollow  wrought- 
iron  drill  rod  with  a  steel  pin  or  expanding  copper  ring.  This 
saved  steel  and  saved  transporting  long,  heavy  drill  rods  to  and 
from  the  blacksmith  shop.  This  bit  was  used  with  the  ordinary 
percussive  air  drill,  and,  in  drilling,  a  small  core  was  formed  which 
broke  up  under  a  slight  blow  on  the  drill  rod.  The  chips  were 
washed  out  of  the  hole  by  a  current  of  water  that  was  forced  down 
through  the  hollow  drill  rod.  The  water  was  introduced  into  the 
hollow  drill  rod,  either  through  the  rotating  bar  or  through  a 
sleeve  surrounding  the  piston  rod  which  was  lengthened  for  this 
purpose;  the  first  method  being  the  best.  Major  Derby  informs 
me  that  the  coarse  chips  of  rock  broken  off  by  the  bit  are  washed 
out  whole,  instead  of  being  reduced  to  dust,  which  saves  power 
and  time  in  drilling  a  hole  of  given  depth.  This  fact  is  well 
shown  by  the  following  comparative  records:  Experiments  were 
conducted  for  several  months  of  actual  work,  during  which  time 
39,119  ft.  of  hole  were  drilled  with  cross-bits  and  39,200  ft.  with  the 
Derby  tubular  bit.  The  holes  were  about  "9  ft.  deep,  and  Rand 
'Little  Giant'  drills  were  used.  As  a  result  of  this  competition 
it  was  found  that  the  tubular  bit  drilled  51  i  per  cent,  faster  than 
the  cross-bit,  and  that  the  diameter  of  the  bottom  of  the  hole  was 
25  per  cent,  greater  than  with  the  cross-bit,  which  in  itself  is  a 
decided  advantage.  Using  a  starter  cross-bit  of  3J  in.,  the  bottom 
of  a  10-ft.  hole  was  2  in.  diameter;  but  with  the  tubular  bit  the 
bottom  was  2?  in.  diameter.  Moreover,  the  tubular  bit  made  a 
perfectly  round  hole,  which  lessens  the  chances  of  a  bit's  stick- 
ing. It  seems  to  me  that  the  greater  speed  of  drilling  with  the 
tubular  bit  was  due  to  the  use  of  a  jet  of  water  to  wash  out  the 


DUST  AND  ITS  PREVENTION  345 

chips,  which  also  accounts  for  the  fact  that  the  bit  does  not  wear 
so  rapidly.  Whatever  the  reason,  the  record  of  excellence  of 
the  tubular  bit  is  well  worthy  of  serious  consideration  by  all  who 
are  interested  in  economic  drilling." 

Why  this  device  which  proved  so  favorable  on  trial  was  not 
put  on  the  market  is  not  stated.  It  may  have  been  that  experi- 
ence showed  that  wear  caused  too  much  leakage  and  that  the 
detachable  bit  itself  gave  trouble. 

General  Conclusions  on  Dust  Prevention.  —  During  a  long 
course  of  actual  underground  work  with  rock  drills  I  came  to 
the  following  conclusions  regarding  this  problem: 

1.  That  an  apparatus  was  required  that  could  be  applied  in 
such  a  way  to  any  ordinary  rock-drilling  machine,  without  alter- 
ing it,  as  to  be  available  when  it  was  necessary  to  drill  a  dry  hole, 
and  allow  the  use  of  ordinary  steel  in  downward  holes.  2.  That 
the  difficulty  of  passing  the  water  from  the  chuck  to  the  jumper 
(drilling  tool)  must  be  avoided.  3.  This  could  only  be  done  by 
making  some  attachment  to  the  drill  stool  outside  the  chuck  of 
the  machine.  4.  This  attachment  must  be  quickly  and  readily 
removed  and  replaced  to  facilitate  change  of  boring  tools.  5.  It 
must  be  attached  in  such  a  manner  as  to  withstand  the  repeated 
and  violent  shocks  caused  by  the  drill  tool  striking  the  rock  and 
must  make  a  proper  water-tight  joint  to  prevent  leakage.  6.  It 
must  be  arranged  in  such  a  manner  as  to  leave  the  drill  tool  clear 
to  strike  and  it  must  not  impede  work  in  any  way.  7.  No 
projections  must  be  made  on  the  drill  tool  that  would  impede 
its  being  withdrawn  past  the  chuck  and  front  head  of  the 
machine  when  it  is  set  up  close  to  the  rock.  8.  The  drill  steel 
must  not  be  weakened  in  any  part,  as  a  fracture  would  sooner  or 
later  develop.  9.  The  apparatus  must  be  simple,  having  few  parts, 
free  from  bolts  and  nuts  liable  to  work  loose,  easily  inspected  and 
repaired,  and  adapted  to  the  most  trying  conditions  of  underground 
work  without  a  large  expenditure  for  maintenance.  10.  The  rota- 
tion of  the  drill  tool  must  not  be  impeded,  as  in  that  case  rifled 
holes  and  poor  results  would  destroy  the  advantage  otherwise 
gained. 

The  advantage  that  would  be  gained  by  the  use  of  such  a 
device  would  be  as  follows:  1.  A  greatly  increased  rate  of  boring 
upper  or  dry  holes,  in  various  cases  from  25  to  100  per  cent.  2. 
The  total  avoidance  of  the  dust  trouble.  The  life  and  comfort 


346  ROCK  DRILLS 

of  miners  would  be  increased  and  the  disease  known  as  "Sili- 
cosis"  would  be  prevented  entirely. 

In  England,  Australia,  and  the  Transvaal,  the  use  of  some 
means  of  allaying  dust  is  rendered  compulsory  by  law.  The  drill 
steel  is  made  in  the  shape  shown,  Fig.  193,  near  the  shank.  The 
tapered  portion  is  swaged  up  and  if  necessary  finished  off  on  a 
lathe.  Starters  and  seconds  are  of  IJ-in.  octagon  steel  with  a 
star  bit;  thirds  and  fourths  are  of  IJ-in.  octagonal  steel,  which 
require  to  be  slightly  jumped  up  before  the  taper  is  formed.  The 
taper  is  from  If  in.  to  1|  in.  in  5  in.,  or  from  If  in.  to  If  in.  in 
3?  in.  for  large  drills.  A  transverse  hole  A,  preferably  of  smaller 
diameter  than  the  hollow  core,  is  bored  right  through  the  drill 
tool  as  shown,  or  merely  drilled  to  meet  the  hollow  core. 

This  weakens  the  steel  and  would,  in  practice,  cause  failure 
of  the  apparatus  through  constant  breakages,  were  it  not  for  the 
way  in  which  the  cylinder  C  makes  a  rigid  joint  on  either  side  of 
it  and  makes  it  the  strongest  part  of  the  drill.  The  cylinder  C 
is  of  the  shape  shown  and  is  bored  out  on  a  taper  corresponding 
to  that  of  the  drill.  The  taper  is  so  arranged  that  the  cylinder 
is  immediately  tightened  on  and  kept  tight  by  the  blows  of  the 
tool  on  the  rock,  but  when  it  is  necessary  to  detach  the  drill 
tool  from  the  machine  owing  to  its  being  blunted,  the  cylinder  is 
easily  and  quickly  detached  by  a  rap  with  a  hammer  and  slipped 
on  another  drill  tool.  This  cylinder  is  bored  out  as  shown  to 
form  a  water  space  U  (enclosed)  between  itself  and  the  drill  tool 
over  the  aperture  of  the  transverse  hole.  It  is  also  pierced  by 
numerous  radial  holes  connecting  the  water  space  U  with  the 
groove  on  its  outside  circumference.  The  packing  is  in  this 
groove.  A  ring  is  hollowed  out  in  the  manner  shown  and  sup- 
plied with  water  by  a  small  hose  clamped  on  to  the  tail  piece  B. 
As  the  drill  tool  and  its  rigidly  attached  cylinder  rotate  within 
this  ring,  the  water  under  pressure,  or  air  and  water  under  pres- 
sure, is  fed  alternately  in  a  continuous  and  intermittent  stream 
through  the  radial  holes,  through  the  water  space,  the  transverse 
hole  in  the  drill,  and  the  drill  core  to  the  cutting  edge  of  the  tool. 
It  will  be  noticed  that  the  edges  of  the  bored-out  space  in  the 
cylinder  are  recessed  to  prevent  their  being  burred  and  that  the 
packing  being  placed  in  the  grooves  cannot  be  dislodged.  It  is 
protected  from  injury  while  it  is  easily  removed  when  worn. 

Two  forms  of  the  apparatus  are  shown,  one  in  which  the  ring 


DUST  AND  ITS   PREVENTION 


347 


B 


H* 5*. *i 


A 

"~r 

0     1 

r^ 

i. 

FIG.  193.  —  Device  for  passing  water  through  drill  steel  to  allay  dust. 


348  ROCK  DRILLS 

is  in  two  parts,  D  (these  parts  are  connected  in  such  a  manner 
by  screws,  split  pins,  and  spring  washers  that  they  cannot  be 
shaken  apart  by  the  vibration  of  the  drilling),  and  the  cylinder 
is  turned  out  of  a  solid  piece,  E.  This  is  the  better  arrangement. 
In  the  other,  the  cylinder  is  made  in  two  pieces  suitably  connected 
and  the  ring  is  cast  solid.  Experiment  has  shown  that  with  a 
water  pressure  more  than  sufficient  to  deliver  the  water  at  the 
end  of  a  long  upper  hole  the  ring  can  be  so  tightly  packed  that 
leakage  is  practically  nil  and  yet  the  rotation  of  the  drill  tool  is 
not  retarded.  The  water  acts  as  a  lubricant  between  the  metal 
and  the  leather.  The  packing  is  in  two  parts,  the  inside  ring 
being  of  soft  rubber  and  the  outside  brass.  The  rotation  of  the 
ring  itself  is  prevented  merely  by  the  weight  of  the  hose  attached 
to  it,  that  it  may  be  loosely  held  by  the  attendant  or  otherwise 
kept  out  of  the  way.  The  " flogging"  of  the  hose  is  not  nearly 
as  severe  as  might  be  supposed  and  there  is  no  great  wear  due  to 
that  cause.  The  apparatus  is  compact,  light,  simple,  and  sub- 
stantial. It  is  proposed  to  provide  the  miner,  working  in  a  drive, 
with  enough  hollow  steel  to  bore  the  dry  holes  or  " upper"  holes, 
and  he  would  employ  them  simply  when  necessary,  boring  the 
rest  of  the  time  with  ordinary  steel. 

Later  experience  showed  that  the  apparatus  in  the  form  shown 
was  not  satisfactory;  the  hollow  core  was  left  open  to  the  end  of 
the  shank  and  combined  with  the  air-jet  device  used  in  Stephens 
Climax  drill.  Holman  brought  out  a  somewhat  similar  device 
combined  with  an  arrangement  to  partially  rotate  the  piston. 

With  these  devices,  and  water  under  very  moderate  pressure, 
holes  may  be  put  in  rapidly,  without  any  great  loss  of  water  or 
any  formation  of  dust. 

Disadvantages.  —  The  drawbacks  to  their  adoption  are  that 
they  are  complicated  and  must  have  intelligent  handling;  that 
it  is  practically  impossible  in  a  mine  to  have  a  regular,  constant, 
and  equal  water  pressure,  available  everywhere;  where  the  pres- 
sure rises  above  about  20  Ib.  to  square  inch  it  is  impossible  to 
avoid  leakage;  with  many  machines  at  work,  the  supply  and  pump- 
ing of  this  water  is  quite  a  serious  matter.  In  practice  the  system 
of  pressure  tanks  gives  endless  trouble  with  most  miners,  and 
water  supplied  under  natural  heads  becomes  choked  with  gravel 
or  dirt.  The  wear  on  the  hose  connecting  these  attachments  is 
severe,  and  hollow  drill  steel  is  expensive.  In  the  case  of  the  first 


DUST  AND  ITS  PREVENTION  349 

apparatus,  forming  the  cone  is  an  additional  expense,  and  in  the 
second  place  is  weakened  by  the  transverse  hole.  Hollow  steel 
gives  trouble  in  welding.  It  must  be  given  very  careful  treat- 
ment as  it  is  usually  high-carbon  steel  and  so  does  not  weld  well; 
in  any  case  welding  and  sharpening  cost  more  than  with__solid 
steel.  If  left  about  the  mine  the  core  tends  to  rust  and  choke. 
I  think  that  an  air  blast  must  always,  as  in  the  Leyner  drill,  be 
mixed  with  water  to  avoid  the  choking  up  and  to  economize 
water.  If  a  detachable  bit  like  the  Anderson  bit  proved  satis- 
factory after  a  long  trial,  the  problem  of  water  injection  would 
prove  somewhat  easier.  The  large  bedring  at  the  end  of  the 
shank  w^jald  make  a  good  water-tight  joint  more  easily  designed; 
the  design  of  some  readily  adjustable  packing  for  the  front  head 
would  render  the  Bornet  system  practicable.  Some  of  the  chief 
rock-drill  manufacturers  have  spent  thousands  of  pounds  experi- 
menting on  this  problem  and  have  not  given  up  hope  of  success. 
An  efficient  water  drill  may  be  on  the  market  at  any  time.  The 
small  Konomax  stoping  drill  is  designed  with  a  water  feed. 

All  the  general  objections  and  difficulties  can  be  overcome  by 
care  and  a -certain  expense;  but  despite  the  terrible  evils  of  pro- 
ducing dust  in  mines,  miners  and  employees  will  refuse  to  employ 
any  machine  that  gives  more  trouble  than  the  present  types, 
unless  the  benefit  in  more  rapid  boring  is  at  once  apparent.  Ex- 
actly what  the  increased  rate  of  boring  down-holes  is  with  water- 
feed  drills  cannot  be  stated.  On  the  Witwatersrand  it  does  not 
seem  as  if  the  increase  is  sufficient  in  boring  down-holes  with 
piston  machines  for  stoping  to  warrant  the  adoption  of  hollow 
steel.  In  recent  trials  the  Siskol  drill  drilled  as  fast  with  hollow 
steel  and  water  injection.  This  is  probably  due  to  the  fact  that 
in  down-holes  in  fairly  hard  rock  the  broken  particles  are  kept 
suspended  in  the  water,  due  to  drill  motion,  and  do  not  lie  at  the 
bottom  of  hole  to  deaden  the  effect  of  the  flow.  In  softer  rocks 
or  in  up-holes  the  difference  would  be  marked,  as  a  flat,  dry  up- 
hole  takes  from  50  to  100  per  cent,  longer  time  to  drill  than  a 
down  or  wet  hole.  This  discussion  has  been  extended  to  show 
inventors  the  lines  on  which  progress  is  possible  and  the  real 
difficulties  that  must  be  met  in  facing  the  problem. 

It  may  be  noted  that  the  introduction  of  an  effective  water- 
feed  device  would  allow  of  a  great  change  being  made  in  the  design 
of  piston  drills.  As  will  be  seen  in  the  chapter  on  "Rock  Drill 


350  ROCK  DRILLS 

Tests,"  there  is  much  evidence  to  show  that  if  there  was  a  means 
of  at  once  ejecting  the  broken  particles  of  rock  from  the  face  of 
the  hole,  a  very  much  shorter  stroke  might  be  used  with  advan- 
tage; this  would  enable  a  shorter  and  lighter  machine  to  be  made 
with  the  same  or  greater  capacity.  A  greater  number  of  lighter 
blows  would  be  struck  per  minute.  The  bit  not  being  withdrawn 
so  far  every  stroke  would  suffer  less  from  frictional  retardation 
in  the  hole,  and  from  wear  on  its  shoulders;  the  work  of  a  piston 
drill  could  be  made  somewhat  more  like  that  of  a  hammer  drill 
and  a  better  efficiency  obtained.  Exhaust  and  inlet  ports  would 
be  shorter,  reducing  clearance  losses  of  air,  and  rendering  reversal 
of  stroke  more  rapid.  The  whole  matter  is  an  economic  one, 
dependent  on  being  shown  in  practice  that  the  added  advan- 
tage in  health  of  workers,  efficiency  in  design  and  operation  of 
machines  are  worth  the  complications  and  expense  caused.  An 
apparatus  such  as  that  designed  by  myself  could,  with  a  machine 
designed  to  take  advantage  of  its  benefits,  be  worked  to  advantage 
only  under  certain  circumstances. 


XVI 
COMPRESSED    AIR 

NOTES  ON  THE  USE  OF  COMPRESSED  Am  AND  STEAM  IN  CONNEC- 
TION WITH  ROCK  DRILL  WORK 

THE  use  of  steam  for  rock  drills  is  confined  to  small  and  tem- 
porary plants  for  quarries  and  surface  excavations.  The  heat  and 
vapor  of  the  exhaust  makes  it  unsuitable  for  use  underground. 
For  the  physical  properties  of  compressed  air  the  reader  is  referred 
to  the  well-known  text-books  on  the  subject.  As  the  problem 
affects  the  mining  engineer  it  may  be  separated  into  three  heads: 

(1)  The  generation  of  compressed  air. 

(2)  The  transmission  of  compressed  air  with  the  minimum  of 
loss  to  the  place  where  it  will  be  employed. 

(3)  Its  most  economical  use  in  rock  drills,  hoists,  and  pumps. 
When  installing  a  compressor  plant  due  regard  should  be  paid 

to  the  probable  life  of  the  mine,  which  involves  the  question  of 
amortization  of  capital  and  the  value  of  the  machinery  when  the 
mine  is  exhausted.  Where  steam  power  is  employed,  and  where 
the  expenditure  is  warranted,  it  is  usual  to  install  two-stage 
compressors  driven  by  cross-compound  engines  having  a  con- 
denser. The  air  cylinders  will  be  jacketed  with  water  and  should 
have  thermometers  attached.  An  inter-cooler  will  be  provided 
with  perhaps  some  arrangement  for  pre-cooling  the  air  before 
compression  and  freeing  it  from  dust.  Ample  facilities  should  be 
provided  for  freeing  it  from  oil  and  water. 

At  elevations  above  sea  level,  air  is  expanded  and  occupies 
more  space  for  a  given  weight,  and  the  capacity  of  an  air  cylinder 
is  reduced.  Hence  the  size  and  cost  of  an  air  compressor  must 
be  increased  at  high  altitudes  to  secure  the  same  output  as  would 
be  maintained  by  the  same  machine  at  sea  level.  This  reduction 
at  5700  ft.  elevation  is  17  per  cent. 

The  Cost  of  Compressed  Air.  —  The  cost  of  steam-generated 
compressed  air  can  be  fairly  accurately  calculated  when  the  fac- 
tors in  any  particular  instance  are  known.  A  good  compound 
condensing  engine  driving  a  compressor  uses  from  14  to  20  Ib. 
of  steam  per  1  h.p.  per  hour.  Efficiency  of  the  air  compressor 

351 


352  ROCK  DRILLS 

may  be  from  80  to  90  per  cent.  The  cost  of  compressed  air  even 
when  generated  from  cheap  coal  forms  a  considerable  item  of 
expense  in  running  a  drill. 

G.  A.  Denny  stated  that  on  the  Rand  one  h.p.  cost  £20  per 
annum,  and  that  only  6  per  cent,  efficiency  was  attained  at  the 
drill.  E.  Laschinger  states  that  the  cost  of  one  steam  h.p.  is 
\d.  per  hour,  and  that  the  cost  of  one  air-horse-power  at  the  drill 
would  be  2d.  Other  records  of  the  horse-power  actually  neces- 
sary to  run  drills  are  given  in  the  chapter  on  rock  drill  tests.  It 
is  influenced  in  any  particular  case  by  the  type  of  drill  employed, 
design  of  pipe  line,  losses  in  leakage;  amount  used  for  ventilation 
after  blasting  which  in  many  cases  is  as  necessary  an  expenditure 
as  running  the  drill.  Leakage  in  a  pipe  system  can  be  kept 
under  5  per  cent.  Laschinger  estimates  that  the  efficiency  of 
power  transmission  from  steam  one  h.p.  at  the  compressor  to 
work  done  at  the  rock  drill  at  80  Ib.  pressure  is  15  to  35  per  cent. 

Air  Consumption  of  Rock  Drills.  —  This  will  vary  with  type  of 
drill,  and  must  not  be  compared  with  the  efficiency  of  the  drill, 
which  is  better  compared  by  air  comsumption  per  inch  drilled  with 
same  diameter  bit.  Figures  for  this  are  given  under  drill  tests.  The 
Sullivan  company  furnishes  tables  for  their  machines.  E.  J.  Lasch- 
inger in  the  Journal  of  the  Trans.  Inst.  of  Mech.  Eng.,  presents 
what  is  perhaps  the  best  modern  practical  discussion  regarding  the 
transmission  of  compressed  air  for  rock  drills  and  I  have  drawn 
largely  from  his  articles  (January  and  March,  1908,  January,  1909). 

He  estimates  the  average  consumption  of  a  3J  in.  drill  at  7 
Ib.  of  air  per  minute  at  75  Ib.  pressure.  This  may  be  reduced 
to  cubic  feet  per  minute  at  any  altitude  by  multiplying  by  the 
number  of  cubic  feet  of  air  weighing  one  pound. 

At  sea  level  13.091  cu.  ft.  air  =  1  Ib. 

At  5700  ft.  15.094  cu.  ft.  air   =1  Ib. 

Notes  on  Installation.  —  In  order  to  conduct  drilling  operations 
at  the  maximum  efficiency  the  mining  engineer  must  first  decide 
on  the  probable  number  and  type  of  rock  drills  to  be  employed 
and  their  probable  air  consumption.  He  must  then  install  a 
compressor  to  provide  this  air  with  a  liberal  and  sufficient  margin 
for  leakage,  ventilation,  and  any  pumps,  hoists,  or  other  machin- 
ery that  may  be  operated  by  compressed  air.  He  must  then 
decide  at  what  pressure  he  wishes  to  work  his  drills.  This  will 
depend  on  the  hardness  and  character  of  the  rock;  cost  of  labor; 
cost  of  compressed  air;  the  distance  the  air  must  be  transmitted; 


COMPRESSED   AIR  353 

the  cost  of  piping  and  other  considerations.  R.  B.  Brinsmade 
writes:  "In  a  certain  mine  using  40  drills  in  hard  fissured  ground 
the  rock  broken  was  increased  40  per  cent,  by  increasing  the  air 
pressure  from  75  to  100  Ib.  A  low-pressure  system  requires 
larger  pipes  for  the  same  power,  and  heavier  pumps  and  hoist  to  do 
the  work  of  a  similar  equipment  working  under  high  pressure." 

Compressed  air  is  transmitted  most  economically  at  high 
pressures.  The  mining  engineer  may  find  it  profitable  to  consider 
the  question  as  to  whether  in  any  given  case  it  might  not  be 
profitable  to  use  the  highest  air  pressures  and  to  reduce  the  force 
of  the  blow,  by  ordering  a  special  drill  with  short  stroke,  or  to  use 
a  machine  with  a  smaller  piston  diameter  than  the  standard 
3J  in.  size.  Experience  has  proved  that  under  most  conditions 
drilling  speed  is  of  primary  importance,  and  it  must  also  be  remem- 
bered that  more  rock  has  to  be  excavated  and  more  work  done  in 
boring  one  hole  of  eight  feet,  than  two  holes  of  four  feet,  because  the 
amount  excavated  will  vary  as  the  square  of  average  diameter  of 
holes.  The  average  diameter  of  a  long  hole  is  much  greater  than 
that  of  two  short  ones.  In  most  cases  air  should  be  supplied  at  the 
drill  at  from  75  to  85  Ib.  pressure.  Where  speed  of  performance  is 
the  vital  consideration,  as  in  shaft  sinking  a  tunnel  driving  work, 
drills  should  be  run  at  the  highest  possible  pressure,  only  regulated 
by  the  manner  in  which  the  drill  bits  and  shanks  behave. 

J.  A.  Vaughan,  in  Trans,  of  South  African  Soc.  of  Mech.  Eng., 
states  that  to  compress  air  to  60  Ib.  requires  28  per  cent,  more 
work  than  to  compress  to  50  Ib.  Used  in  a  rock  drill  with  60  Ib. 
the  number  of  strokes j^er  minute  increases  as  the  square  roots  of 
the  pressures  or  as  \/60  to  \/50  or  1.106  to  1.01,  equal  to  10  per 
cent,  increase.  Work  done  in  drilling,  or  the  Kinetic  energy,  de- 
veloped by  the  same  mass,  varies  as  square  of  velocity,  and  this 
varies  directly  as  the  pressure  or  as  60  to  50  =  1.2  to  1.  The 
total  work  done  in  boring  increases  from  1  to  1.2  X  1.106  =  100 
to  132  or  32  per  cent,  increase.  This  is  borne  out  by  actual  trials. 

If,  however,  air  is  compressed  to  80  Ib.  and  delivered  to  drill 
at  60  Ib.  and  at  50  Ib.,  the  loss  of  efficiency  from  60  to  50  Ib.  is 
13.4  per  cent,  and  from  80  to  50  Ib.  is  much  greater. 

Transmission  of  Air.  —  The  mining  engineer  must  now  make  an 
estimate  of  the  maximum  distance  air  must  be  transmitted,  and  also 
the  average  distance.  He  will  design  his  pipe  line  to  make  the  loss 
of  pressure  in  transmission  as  low  as  possible  consistent  with  a 
reasonable  expenditure  on  pipe  service.  Losses  in  transmission 


351 


ROCK  DRILLS 


should  roughly  balance  loss  of  interest  and  amortization  in  capital 
expended  on  his  pipe  lines;  but  the  loss  of  pressure  must  be  kept 
low.  It  must  be  remembered  that  when  air  is  delivered  at  a  lower 
elevation  than  that  of  the  compressor  its  pressure  increases. 

Laschinger  gives  the  following  table  showing  increase  in  pres- 
sure at  varying  depths  at  80°  F.     If  top  pressure  equals  1,  at 
500  ft.  the  pressure  is  1.01755 
800  ft.  the  pressure  is  1.02823 

1000  ft.  the  pressure  is  1.03541 

1500  ft.  the  pressure  is  1.05358 

2000  ft.  the  pressure  is  1.07206 

2500  ft.  the  pressure  is  1.09090 

3000  ft.  the  pressure  is  1.11003 

3500  ft.  the  pressure  is  1.1295 

4000  ft.  the  pressure  is  1.14933 

5000  ft.  the  pressure  is  1.19003 

At  "3000  ft.  11  per  cent,  more  drills  can  be  run  or  the  same 
number  of  drills  at  11  per  cent,  higher  pressure  with  same  air  as 
at  the  surface,  assuming  that  an  air-horse-power  underground  is 
worth  2d.  per  hour,  and  that  the  total  cost  of  laying  piping  is 
according  to  the  following  table  by  Laschinger: 

TABLE  I.    COST  PER  FOOT  FOR  INSTALLING  AIR-PIPE  LINES  ON  THE  RAND 


Nominal  Size  Pipe 
Inches 

Surface 

Underground 

1 

s. 

0 

d. 

9 

s. 
1 

d. 

0 

11 

1 

0 

1 

4 

t| 

1 

3 

1 

8 

2 

1 

9* 

2 

5 

2i 

2 

4 

3 

2 

3 

2 

111 

3 

11 

3* 

3 

7 

4 

10 

4 

4 

3 

5 

8 

4i 

4 

11 

6 

6 

5 

5 

7 

7 

6 

6 

7 

1 

9 

5 

7 

8 

6 

11 

5 

8 

10 

1 

13 

6 

9 

11 

9 

15 

7 

10 

13 

4 

17 

10 

12 

16 

9 

22 

4 

14 

20 

4 

27 

1 

COMPRESSED    AIR 


355 


Laschinger  points  out  that   higher   velocities   are   allowable 
in  larger  pipes  and  that  the  velocities  here  shown  are  not  excessive. 


TABLE  II.     SHOWING  MOST  ECONOMICAL  NUMBER  OF  3|-lNCH  DRILLS 
SERVED  BY  STANDARD  PIPES  AND  MEAN  VELOCITY  OF  AIR     — 


Nominal 
Size 
Pipe 
Inches 

Internal 
Diameter 
Inches 

Surface  Mains 

Shaft  Mains 

Distributing  Pipes 

Number 
of 
Drills 

Mean 
Velocity 
Feet  per 
Second 

Number 
of 
Drills 

Mean 
Velocity 
Feet  per 
Second 

Number 
of 
Drills 

Mean 
Velocity 
Feet  per  , 
Second 

1 

1.05 

0.46 

19.1 

0.51 

21.1 

0.64 

26.6 

ii 

1.38 

0.85 

20.5 

0.94 

22.6 

1.18 

28.4 

It 

1.61 

1.21 

21.3 

1.33 

23.5 

1.67 

29.6 

2 

2.07 

2.12 

22.7 

2.34 

25. 

2.94 

31.5 

2t 

2.47 

3.16 

23.7 

3.48 

26.1 

4.37 

32.9 

3 

3.07 

5.15 

25.0 

5.17 

27.6 

7.14 

34.7 

3} 

3.55 

7.15 

26.0 

7.86 

28.6 

9.91 

36. 

4 

4.03 

9.5 

26.8 

10.5 

29.5 

13.2 

37.2 

41 

4.51 

12.2 

27.5 

13.5 

30.3 

17.0 

38.2 

5 

5.05 

15.8 

28.4 

17.4 

31.2 

21.9 

39.4 

6 

6.07 

23.8 

29.7 

26.3 

32.7 

33.1 

41.4 

7 

7.02 

33.1 

30.8 

36.5 

33.9 

45.9 

42.7 

8 

7.98          44.2 

31.8 

48.6 

35. 

9 

8.94 

57.1 

32.7 

62.8 

36.1 

10 

10.02 

73.8 

33.7 

81.0 

37.1 

12 

12. 

111. 

35.2 

122. 

38.8 

14 

14. 

157. 

36.6 

172. 

40.3 

Laschinger  gives  in  Table  II,  the  most  economical  size  of  pipe 
to  use,  for  any  reasonable  distance  in  mining  work.  The  size  of 
pipe  given  is  that  which  under  these  costs  makes  the  capital  in 
pipe  line  equal  the  value  of  power  lost,  while,  at  same  time,  loss 
of  pressure  is  within  reasonable  limits. 

He  also  points  out  that  if  the  cost  of  installing  pipes  be  doubled 
or  halved  the  resulting  diameter  of  pipe  is  only  decreased  or  in- 
creased by  about  11  per  cent,  and  inversely  for  the  same  varia- 
tions in  cost  of  power. 

This  establishes  tables  of  value  where  these  costs  can  be  esti- 
mated, and  the  results  hold  good  for  pressures  from  40  to  80  Ib. 
gage  per  square  inch. 

It  must  be  remembered  that  pipe  fittings  increase  resistance 


356  ROCK  DRILLS 

72 
to  flow  of  air  in  pipes.     When  —  =  velocity  head,  the  equivalent 

length  of  pipe  to  which  could  be  attributed  the  loss  by  friction  of 
the  energy  of  velocity  head,  would  be, 

Length  of  pipe  in  feet  =  —  (value  of  constants  below). 

Taking  this  equivalent  length  of  pipe  as  1,  the  resistance  due 
to  fittings  Laschinger  gives  as  follows: 

Air  receiver,  2.5;  entrance  head,  1.5;  sharp  elbow,  2.0;  round 
elbow,  1.0;  easy  bend,  0.2;  tee,  2.0;  globe  valve,  4.0;  angle  valve, 
2.5;  gate  valve,  0.2;  cock,  0.5. 

It  will  be  seen  that  sharp  bends  and  globe  valve  should  be 
avoided  as  much  as  possible,  and  gate  valves  or  full-way  valves 
used  on  pipes  down  to  3-in.  size. 

Laschinger  gives  the  following  formulae  which,  when  the  weight 
of  air  required  per  second  at  the  end  of  any  pipe  line  is  determined, 
will  enable  any  particular  case  to  be  checked  with  the  tables : 

When  W=  Ibs.  weight  of  air  delivered  per  second; 
d  =  internal  diameter  of  pipe  in  inches; 
Pi=  initial  pressure  in  pounds  per  square  inch  absolute; 
p2=  final  pressure,  absolute;  absolute  pressure  equals 

gage  pressure  +  atmospheric  pressure. 
T  =  'absolute  temperature  =  (Deg.  F.  +  460.7) 
L  =  Length  of  pipe  in  feet. 
R  =  constant  for  air  =  53.22. 
TT  =  3.14159. 

0.03 
z  =  0.005  +  ~p-  (Laschinger's  formulae). 


v  =  mean  velocity  of  flow  in  feet  per  second. 
Then, 

W  =  0.17625 


zLT 
2.0024 


v  =  23.886 


zL(pt 

V/  p  2  —  3  2 


COMPRESSED    AIR  357 

MAINTAINANCE  OF  PIPE  LINES  AND  AIR  HOSES. 

Drainage  pockets  to  collect  condensed  water  should  be  in- 
stalled at  suitable  points  having  automatic  discharge,  or  valves 
which  must  be  opened  at  regular  intervals.  Pipes  should  be-  laid 
so  as  not  to  be  covered  by  mud  and  water.  They  should,  in 
sizes  above  3  in.,  be  bent  at  the  surface,  to  the  curve  required. 
They  should  be  carefully  bent  while  hot  to  avoid  excessive  con- 
traction of  area.  They  should  be  of  the  best  quality  obtainable. 
Mr.  Cullen  found  seamless  piping  to  be  most  suitable  for  under- 
ground work  along  levels.  Special  cocks  for  attaching  pressure 
gages  at  important  points  should  be  put  in.  When  a  pipe  is 
broken  and  the  usual  connection  is  made,  care  must  be  taken 
that  the  rubber  insertion  for  joint  does  not  project  into  the  pipe. 
Plug  or  cone  valves  should  be  used  at  hose  connections. 

Large  underground  reservoirs  are  often  a  great  help  in  regu- 
lating pressure,  and  assisting  the  compressor. 

Leakage  in  shaft  mains  are  frequent,  and  are  due  often  to 
the  weight  of  pipe  not  being  properly  taken  up.  The  alternate 
exhaustion  and  contraction  of  pipe  for  about  500  ft.  down  the 
shaft  due  to  passage  of  hot  air  while  the  compressor  is  working 
and  the  cooling  when  compressor  is  stopped  is  liable  to  cause 
leaks.  Soap  solution  poured  into  pipes  before  testing  for  leak- 
age shows  up  small  leaks  by  blowing  out  bubbles.  Oil  and  red 
lead  should  be  used  for  screwed  joints. 

Rock  Drill  Hose.  —  A  3i-in.  drill  for  pressure  above  40  Ib. 
requires  a  hose  of  larger  diameter  than  one  inch.  The  loss  of 
pressure  is  6  Ib.  to  the  square  inch  in  50  ft.  of  one  inch  hose 
when  running  a  3|-in.  drill  at  70  Ib.  pressure.  One  and  one- 
eight  inch  hose  is  now  sold  on  the  Rarid.  Good  hose  is  hard  to 
obtain,  as  the  filling  used  with  the  rubber  is  usually  excessive  in 
quantity. 

Beware  of  cheap  hose,  as  it  causes  numerous  losses  owing  to 
leakage;  stoppage  of  air  owing  to  the  buckling  up  of  the  lining, 
and  to  its  short  life.  Pay  for  the  best  article  —  arid  see  that  the 
quality  is  there.  The  inner  lining  of  a  good  hose  should  be  with- 
out a  longitudinal  joint.  The  rubber  should  be  soft,  pliable,  and 
of  a  good  color.  The  nature  and  quantity  of  filling  used  should 
be  specified  and  checked  by  analysis  where  possible. 

All  hoses  in  the  mine  should  be  examined  and  tested  frequently 


358  ROCK    DRILLS 

to  see  that  leakage  is  not  excessive;  that  they  are  not  seriously 
dented,  or  the  area  of  air  way  otherwise  contracted.  Economy 
in  expenditures  here  increases  mining  costs.  Acid  mine  water 
attacks  the  wire  armoring  and  rots  the  outside  of  the  hose,  while 
oil  from  the  compressor  softens  the  rubber  lining.  Hose  for  min- 
ing work  may  be  either  armored  with  well  galvanized  wire  or 
completely  unarmored.  Marline  wound  hose  is,  I  consider, 
unsuitable  for  mining  work,  as  any  injury  causes  the  marline  to 
ravel.  Wire  protects  the  hose;  but  retains  dents,  reducing  the 
area  of  internal  tube. 

It  is  well  to  try  both  kinds  of  hose  and  compare  them  under 
the  special  conditions  of  the  case. 

CONCLUSION 

In  conclusion,  if  I  were  to  sum  up  the  lessons  forced  on  my 
attention  during  rny  practical  experience,  with  rock  drills  pipe 
lines,  and  hoses  in  one  word,  the  word  used  would  be  maintenance. 
The  engineer  must  employ  expensive  labor,  surface  equipment, 
and  use  expensive  power  to  operate  what  is  at  its  best  an  ineffi- 
cient machine  to  do  the  most  important  work  of  the  mine. 

If  he  stints  his  expenditure  in  money,  time,  and  constant 
personal  supervision,  and  the  whole  system,  from  compressor  to 
drill,  is  not  maintained  at  the  highest  possible  efficiency,  the  result 
of  his  neglect  will  most  surely  reveal  itself  in  high  mining  costs. 


INDEX 


Aberdeenshire,     granite     quarrying, 

264. 

Abrasion  in  rock  drilling,  129. 
Adams  electric  drill,  91,  92,  93,  94. 
Adelaide  drill,  11. 
Air,  calculation  of  volume,  318. 
compressed,  137. 

Caledonia  mine,  272. 
cost,    351. 

in  rock  drill  work,  351. 
installation,  352. 
consumption,  316,  320,  327,  352. 
of  hammer  drills,  82. 
Rose  deep  mine,  324. 
drill,  electric,  95. 
results,  94,  95. 
test,  90. 

versus  electric  drills,  102. 
economizing,  122. 
-fed  drills,  49,  50. 

-hammer  drill,  64,  65. 
feed,  "Cleveland"    hammer   drill, 

75. 

hose,  handling,  241. 
maintenance,  357. 
losses,  327. 

mean  velocity,  355,  356. 
practice,  332. 
pressure,  252. 

electric  air  drill,  98. 
tightness  test,  146. 
transmission,  352. 
valve  drills,  24. 
Ajax  drill  sharpener,  157. 
Allgemeine  Electricitats  Gesellschaft 

electric  furnace,  152. 
America,  rock  drill  practice,  269. 
Anderson  detachable  drill,  169,  170. 
Anvil    Block    Machine    Co.'s    false 
chuck,  78. 


Anvil-block  machines,  78. 
"Arc  Valve"  tappet  drill,  13. 
Arm,  correct  position,  108. 

maintenance,  146. 
Atlas  powder,  179. 
Australia,  rock  drill  practice,  258. 
Auxiliary  valve  drills,  31. 

Bar,  bad  arrangement,  107. 
double-jack,  109. 
drill,    arrangement    in    bottom    of 

shaft,  241. 
jack,  40. 

maintenance,  146. 
mounting  drill  on,  in  stope,  111. 
position,  108,  109. 
rifle,  of  hammer  drill,  53. 
stoping,  64. 

Battery  blasting,  cautions,  202. 
Bench,  hight  compared  with  size  of 

hole,  222. 

Bits,  broken-off,  recovering,  239. 
changing,  114. 
chisel,  163. 

sharpening,  156. 
of  grooved  steel,  166. 
correct  drill  (Leyner),  172. 
cross  vs.  chisel,  317. 
cruciform,  sharpening,  157. 
detachable,  168. 
drill,  150,  151,  166. 
American  system,  154. 
design  and  shape,  162. 
South  African  system,  155. 
for  hammer  drills,  173. 
forged   by   Word   drill   sharpener, 

167. 

Holman  Bros.,  167. 
shaping,  American  practice,  163. 
star,  163,  166. 


359 


360 


INDEX 


Bits  used    with    air-hammer    drills, 

176. 

Blast,  conditions  affecting,  312. 
Blasting,  114,  182. 

Aberdeenshire,  267. 

Caledonia  mine,  271. 

cautions  regarding  battery,  202. 

conditions  influencing,  211. 

Davis  mine,  278. 

Golden  Horseshoe  mine,  262. 

in  heavy  rock  excavation,  311. 

suggestions,  195. 

with  high  explosives,  210. 
Blasts,  premature,  194. 

smoky,  194. 
Blocks,  105. 

Blow,    determining    absolute    force, 
316. 

determining  number,  315. 

electric  air  drill,  99. 

how  delivered  by  hammer  drill,  50. 

kinetic  energy  of,  138. 

nature  of,  in  rock  drilling,  129,  130. 

of  hammer,  taking  up,  80. 
Boring  rock,  systems,  129,  130. 

speed,  332. 
Bornet  hollow  drill  bit,  343. 

system  for  using  hollow  drill  steel, 

342. 

Box  electric  drills,  95. 
Broken  Hill,  rock  drill  practice,  260. 
Brunton's  "Wind  Hammer,"  2. 

Caledonia  mine,  drill  practice,  269. 
Caps,  blasting,   184,   186,   188,   189, 

194,  196. 

correctly  placed,  195. 
proper  placing  of,  196. 
Carnahan  Mfg.  Co.'s  Murphy  Stand- 
ard drill,  61,  62,  63. 
Carriages,  rock  drill,  43. 
Center  Star  mine,  rock-drilling  prac- 
tice, 284. 
Charges,  formula  for  calculating,  219. 

length,  225. 
Charlton  and  Meyer,  rock  drill  tests, 

330. 
Chersen  ball  valve  drill,  47. 


Chersen  chuck,  47. 

drill,  333. 
Chicago  Giant  rock  drill,  16. 

Pneumatic    Tool    Co.,    rock    drill 

oiler,  118. 
Chipping  system  of  rock  drilling,  129, 

130. 

Chronology  of  rock  drilling,  5. 
Chuck  bushings,  renewing,  145. 
false,  of  Anvil  Block  Machine  Co., 

78. 

drill,  45. 

hammer  drill,  53. 
maintenance,  144. 
Churn  drilling,  136. 
Clamp,  drill,  39. 
maintenance,  146. 
to    extract    drills    from    fitchered 

holes,  239. 

Cleveland  hammer  drills,  58, 60, 74, 75. 
Climax  Imperial  drill,  333. 
spray,  340. 

tappet  valve  drill,  23. 
Colors  of  steel  at  different  tempera- 
tures, 150,  153. 

Column,  double  screw  tunnel,  40. 
Combustion  differentiated    from  ex- 
plosion and  detonation,  185. 
Conditions  under  which  rock  drills 

work,  133. 
Connections,  machine,  maintenance, 

146. 

Construction  of  machine,  131. 
Contests,  rock  drill,  315. 
Corliss  valve  drills,  30. 
Costs,  air,  per  rock  drill  per  shift,  149. 
breaking  and  shoveling  rock,  248. 
compressed  air,  351. 
drifting,  Lake  Superior,  297. 

South  Africa,  227. 
excavating,  314. 
explosives,  280. 

generating  compressed  air,  122. 
installation  of  air-pipe  lines,  354. 
machine  drilling,  280,  283. 
operating  rock  drill,  132. 
per    foot    for    installing    air-pipe 
lines,  218. 


INDEX 


361 


Costs,  running  machines  in  stoping, 

256. 
shaft  sinking  with  machines,  South 

Africa,  237. 
sinking  shafts,  243. 
stoping,  298,  299. 
with  electric  drill,  90. 

hammer  drill,  83. 
Cradle,  attaching  drill  to,  110. 
drills,  49. 

guides,  wear  on,  142. 
Sullivan,  39. 
Crimper,  191,  192. 
Crimping,  191. 
Cripple  Creek  practice'  in  use  of  bits, 

175. 

Cross-bits  versus  chisel  bits,  317. 
Cut,  channeling,  233,  234. 

triangle  and  V,  258. 
Cylinder,  valveless  air-hammer  drill, 

79. 

boring  out,  148. 
maintenance,  141. 
Cylindering,  back,  of  hammer  drill,  53. 

D  15  Sullivan  hand  hammer  drill,  60. 
19  Sullivan  hand  hammer  drill,  61. 
Darlington  drill,  10,  11. 
Davis    pyrites    mines,    Mass.,    rock 

drill  practice,  273. 
Deitz  electric  drill,  87,  88. 
Denver    Rock    and     Machine    Co., 

Waugh  drill,  76,  77. 
Derby  tubular  bit,  344. 
Design  of  hammer  drills,  80. 
Detonation,    differentiated   from   ex- 
plosion and  combustion,  185. 
of  high  explosives,  183. 
procuring  complete,  194. 
Detonators,  183,   196. 

results  obtained  from  strong  and 

weak,  189. 
selection,  188. 
Development,  221. 

future,  of  rock  drills,  334. 

report,  Portland  Gold  Mining  Co., 

278. 
Drift  stoping,  Joplin,  307. 


Drift  stoping,  Wolverine  mine,  292. 
Drifting,  Caledonia  mine,  269,  270. 

Joplin,  304. 

Lake  Superior,  295. 

South  Africa,  227. 

Driving,  record,  in  Rand  deep  levels, 
231. 

West  Australia,  258. 
Dunstan's  drill  sharpener,  158. 
Durban  Roodeport,   driving  results, 

232. 
Dust,  338. 

preventers,  disadvantages,  348. 

prevention,  338,  345. 

produced  in  rock  drilling,  effects, 

339. 
Dynamite,  178,  179. 

storehouse,  181. 

East  Rand  Extension,  driving  results, 

232. 

•'Eclipse"  drill,  24,  25. 
Efficiency  of  drill,  131. 
Electric  air  drill,  95. 

air  drill,  advantages,  101. 
drill,  disadvantages,  102. 
drill,  results,  101. 
current  for  electric  air  drill,  99. 
drills,  85. 

results,  90,  91,  94,  95. 
rotary,  94. 
test,  89,  90. 
versus  air  drills,  102. 
firing  versus  fuse  firing,  203.     . 
shot  firing,  197. 
Energy  loss,  137,  138,  139. 

of  blow,  kinetic,  138. 
Eureka  Steel  Drill  Co.'s  drill,  168. 
Europe,  hammer  drills,  65. 
Excavation,  Aberdeenshire,  265. 

of  rock  in  large  masses,  309. 
Explosion,  causes,  112,  117. 

differentiated  from  combustion  and 

detonation,  185. 
Explosives  and  their  use,  178. 
choice  of,  208. 
force  generated  by,  212. 
Golden  Horseshoe  mine,  263. 


362 


INDEX 


Explosives,  high,  108,  210,  206. 

detonation,  183. 

effect,  214,  215. 
low,  178,  216. 

Portland  Gold  Mining  Co.,  281. 
thawing,  180. 

Face  working  in  to  cut  pillar  from 

above,  254. 

Feed-screws,  maintenance,  146. 
Feeding  forward  of  machine,  116. 
Findley   Consolidated   Gold   Mining 
Co.,  rock-drilling  practice,  285. 
Firing,  electric  versus  fuse,  203. 

West  Australia,  259. 
Fitter,  147. 
Fittings,  drill,  39. 
Fluids,  statics  of,  216. 
Foot  block  with  steel  plate,  105. 
Foote,  D.  A.,  30. 

torpedo  drill,  31. 

Force  generated  by  explosives,  212. 
Forcite,  179. 
Forges,  151. 
Fowle,  J.  W.,  2. 

Frame,  drill,  for  boring  breast  shot- 
holes,  266. 

shaft-sinking,  43,  44. 
Friction  losses,  137. 
Furnaces,  heating,  151. 
Fuse,  correctly  placed,  195. 

cut  wrongly,  195. 

electric,  190. 

good  and  bad  forms  of  inserting  in 
caps,  191. 

igniting,  205. 

poorly  placed,  194. 

proper  care,  193. 

swaging  end,  196. 

testing,  201. 

versus  electric  firing,  203. 

wrapped  with  adhesive  tape,  194. 

Gardner  electric  drill,  88. 

Gases   resulting   from   nitroglycerine 

explosives,  206. 
statics  of,  216. 
Gasolene  rock  drill,  104. 


Gassing,  207. 

Gear,  rotating;  maintenance,  144. 

Gelatine,  blasting,  179. 

dynamite,  179. 
Gelignite,  178. 
German  device  for  preventing  dust, 

342. 

Golden  Horseshoe  mine,  West  Aus- 
tralia, 262. 

Gordon  air-hammer  drill,  55,  57,  58. 
Granite,  excavation  costs,  314. 

quarrying,  Aberdeenshire,  264. 
Ground,  hard,  drilling,  113. 
Group  electric  shot  firing,  197. 
Guide,  Sullivan,  39. 
Gunpowder,  178. 

charging  with,  182. 

Hammer  drills,  49,  138. 
drills,  advantages,  81. 
design,  80. 
Europe,  65. 
hand,  58. 
maintenance,  147. 
South  Africa,  226. 
types,  65. 

used  on  stoping  bar,  64. 
of  hammer  drill,  53. 
type  in  which  vanadium  steel  is 

used,  79. 

versus  piston  drills,  136. 
Hand  drilling,  309. 
drills,  49. 
hammer  drills,  58. 
Hard  ground,  drilling  in,  113. 
Hardscogg  drill,  173. 

"Little     Wonder"     trigger    valve 

drill,  62. 

"Wonder"  air-hammer  drill,  73. 
Wonder  drills,  174. 
Hardy  Simplex  hammer  drill,  58,  59. 
Heads,  back,  maintenance,  144. 
back  of  hammer  drill,  53. 
front,  maintenance,  144. 
Heat  treatment  of  high-carbon  steel, 

153. 

Heating  drills,  151. 
Hercules  powder,  179. 


INDEX 


363 


Hints  for  operator,  116. 
History  of  rock  drills,  1. 
Hitches,  Davis  mine,  275. 
Holes,  arrangement,  282. 

arrangement  for  breaking  ore,  308. 
in  drift  stoping,  298. 
in  ordinary  ground,  229. 
in  raise  stoping,  298. 
in  removing  pentice,  301. 
in  shaft  sinking,  301,  304,  305. 
Lake  Superior,  297. 
Ophelia  tunnel,  288. 
South  Africa,  227,  228. 
Wolverine  mine,  294. 
cut,  arrangement,  233. 
cylindrical,  217. 
diameters,  217,  218. 
drift,  arrangement,  306. 
in  bottom  of  winze,  229. 
length,  221,  246,  247. 
long  versus  short,  223. 
numerical    order    of    drilling    with 
multiple  arrangement  of  drills, 
230. 

old,  112. 

proper  depth,  214. 
ratio  of  depth  to  diameter,  218. 
size  compared  with  height  of  bench, 

222. 

starting,  111,  112. 
Holman  auxiliary  ball-valve  drill,  33, 

34. 

auxiliary  valve  drill,  31,  32,  33,  34. 
Brothers  drill  bits,  167. 
chuck,  47. 

ratchet  and  pawls,  36. 
spray,  340. 
tappet  drill,  23. 
2i-inch  drill,  334. 
2J-inch  drill,  333. 

2-inch  diameter  5-inch  stroke  work- 
ing underground,  251. 
Horse-power  tests,  325. 
Horsfield's  "National"  tappet  drill, 

20,  21,  22. 

new  type  of  Ingersoll  drill,  26,  27. 
Hose,  106. 

connections,  111. 


Hose,  maintenance,  357. 

rock  drill,  357. 

Hot- time  lateral,   Newhouse  tunnel, 
rock-drilling  practice,  285. 

Ignition  of  powder  charge,  183. 
Imperial    drill    boring    with    hollow 

steel,  251. 

Indicator  cards,  147. 
Ingersoll  auxiliary  valve  drill,  31,  32, 

33. 

drill,  HorsfiekTs  new  type,  26,  27. 
" Eclipse"  drill,  24,  25. 
-Rand  chuck,  48. 

drill,  13. 

-Sergeant  chuck,  45. 
drill,  31,  273. 
rock  drill  column,  40. 
versus  Konomax  drill,  328. 
Installation,  compressed  air,  352. 

Jack,  maintenance,  146. 

stools,  maintenance,  146. 
James's  water  blast,  342. 
Joints,  maintenance,  146. 
Joplin,  Mo.,  rock-drilling  practice,  301. 
Judson  powder,  179. 

Kalgoorlie  field,  rock  drill  practice, 

260. 

Kid  drill,  16. 
Kimber  air-hammer  drill,  55,  56,  58. 

t  drill-sharpening  machine,  160. 
Konomax  drill,  125. 

versus  Ingersoll  drill,  328. 

Leakage  in  shaft  mains,  357. 

of  air  hose,  117. 
Leyner  correct  drill  bits,  172. 

drill,  136,  173. 

George,  oiler,  119. 

hammer  drill,  water,  51,  52. 

patent  starter,  172. 

Rock  Terrier  drill,  54,  55. 

water  drill,  Davis  mine,  277. 
Little  Giant  rock  drill,  13,  276. 

Hardy  rock  drill,  25. 

Jap  hammer  drills,  277. 


364 


INDEX 


Little  Wonder  air-hammer  drills,  277. 

trigger  valve  drill,  62. 
Loading,  312. 
Locke  electric  drill,  89. 
Lockers,  105. 
Logging  repairs,  146. 
Long   Tunnel   mine,   sinking  incline 

shaft,  264. 

Loosening  ground,  Utah,  308. 
Losses,  air,  327. 
Lubricating  devices  for  rock  drills,  1 18. 

McKiernan  drills,  Davis  mine,  276. 

drills,  Caledonia  mine,  271. 
Machine  drilling,  309. 

drilling  in  hard  rock,  238. 
sizes,  278. 

drills,  Davis  mine,  276. 

for  using  hollow  drill  steel,  342. 
Maintenance  of  hammer  drills,  147. 

of  pipe  lines  and  air  hose,  357. 

rock  drills,  141. 
Marvin  Sandy  croft  drill,  85. 
Masks,  340. 

Materials  in  piston  rock  drills,  48. 
Maynard  chuck,  46. 
Meyer  and  Charlton,  rock  drill  tests, 

330. 
Michigan   copper   mines,    details   of 

drilling,  296. 

Miners,  differences  in,  234. 
Mining,  first  drill  used,  2. 
Misfires,  247. 

and  how  to  avoid  them,  190. 
Modderfontein     "B"     gold     mines, 

driving  results,  232. 
Mohawk  bit,  165. 
Mountings,  drill,  39. 
Muck  as  staging,  287. 

handling,  289. 
Mucking,  244. 

Ophelia  tunnel,  288. 
Murphy  drill,  tank,  339. 

Number  2  hammer  drill,  70,  71. 

Standard  drill,  61,  62,  63. 

steel  drills,  173. 

"National"  tappet  drill,  20,  21,  22. 


New  Century  00  drill,  334. 

Ingersoll   rock   drills,    work   done, 

262. 
Modderfontein,      driving     results, 

233. 

Newhouse  tunnel,  rock-drilling  prac- 
tice, 285. 

Nitroglycerine,  179. 
Numa  drill  sharpener,  157. 
Number  0  drill,  16. 

of  3i-inch  drills  served  by  standard 

pipes,  355. 
Nuts,  maintenance,  146. 

Oilers,  rock  drill,  118. 

Oiling,  110. 

Ophelia    tunnel,    rock-drilling    prac- 
tice, 286. 

Optimus  compound  rock  drill,   123, 
124. 

Ore,  breaking,  Joplin,  307. 
Davis  pyrites  mine,  273. 
extraction  system,  Caledonia  mino, 
270. 

Orebody,  Joplin,  307. 

Overheating  drill  bits,  156. 

Pawls  of  hammer  drill,  53. 
Percussion  drills  versus  rotary  pres- 
sure drills,  134. 
electric  drill,  85. 
in  rock  drilling,  129. 
Philosophy    of    process    of    drilling 

rock,  129. 
Pillars  in  quarry  stope,  Rose  Deep, 

250. 

Pipe  fittings,  355. 
lines,  106. 

maintenance,  357. 
serving  31-inch  drills,  355,  356. 
sizes,  355. 
Piston  drills,  8,  342. 
drills,  classification,  10. 

designed  to  use  air  exclusively, 

122. 

South  Africa,  226. 
electric  air  drill,  100. 
maintenance,  144. 


INDEX 


365 


Piston  rock  drills,  35. 

rods,  maintenance,  144. 

versus  hammer  drills,  136. 

wear  of,  142. 
Plan  of  work,  108. 
Plate,  rotating,  of  hammer  drill,  53. 
Plunger,    pawl    spring,    of    hammer 

drill,  53. 
Portland    Gold     Mining    Co.,    rock 

drill  practice,  278. 
Powder  charge,  ignition,  183. 

conditions  influencing,  186. 

diameter  of  sticks,  187. 

explosive  force,  185. 

fumeless,  186. 

maximum  strength,  how  produced, 
183. 

storage,  194. 

susceptibility  to  detonation,  184. 

Rack-a-Rock,  179. 
Raise  stoping,  Wolverine  mine,  294. 
Rand  Collieries,  Ltd.,  geological  sec- 
tion of  diamond  drill  hole,  235. 
deep  levels,  record  driving,  231. 
"  Little  Giant,"  13,  276. 
Model  No.  5  drill,  15. 
"Slugger"  rock  drill,  29. 
Repairs,  117. 
logging,  146. 
made  by  contract,  141. 
rock  drill,  141. 
Reshanking  drills,  145. 
Resistance  due  to  pipe  fittings,  356. 
Respiration,  artificial,  208. 
Respirators,  340. 
Rifling,  320. 
Rock-boring  systems,  129,  130. 

character  of,  Rand  Collieries,  Ltd. 

235. 
drilling,  Aberdeenshire,  266. 

practice  in  heavy  rock  excava- 
tion, 310. 
drills,  1. 

contests,  315. 

future  development,  334. 

hose  for,  357. 

in  tunnels,  291. 


Rock  drills  of  1880,  3. 

practice,  America,  269. 
practice,  Broken  Hill,  260. 
practice,  examples,  226. 
tests,  315,  321,  322,  323,  325,  330. 
used  in  South  Africa,  226. 
Witwatersrand,  226. 
Rockers,  maintenance,  144. 
Roosevelt     drainage     tunnel,     rock- 
drilling  practice,  290. 
Rose   Deep,  three   pillars  in  quarry 

stope,  250. 
Rotary  electric  drills,  94. 

pressure    drills,    versus    percussion 

drills,  134. 
Rotation,  81. 

Adams  electric  drill,  93. 
modified  slip,  36. 
systems,  hammer  drills,  50. 

piston  rock  drills,  35. 
Rubislaw   quarry,    showing   working 

face,  265. 
Running  of  machine,  116. 

Schram,     Harker    &    Co.,    Optimus 
compound  rock  drill,  123,  124. 
Scotland,  rock  drill  practice,  264. 
Scott  gasolene  rock  drill,  104. 
Sergeant  drill,  section  showing  parts, 

8. 

rock  drills,  descriptive  table,  9. 
slip  rotation,  35. 
Set-up,  106,  107,  108. 
Setting  the  machine,  110. 
Shaft,  inclined,  sinking,  248. 

Number  1,  Rand  Collieries,  Ltd., 

236. 
sinking,  Caledonia  mine,  270. 

Davis  mine,  278. 
•      frames,  43,  44. 
Joplin,  303. 

Long  Tunnel  mine,  264. 
method,  V-cut,  259. 
rapid,  with  air  drills,  245. 
sump  and  bench  system,  244. 
the  Rand,  235. 

Victoria    Reef    Quartz    Mining 
Co.,  263. 


C66 


INDEX 


Shaft  sinking  with  machines,  236,  242. 

Wolverine  mine,  300. 
Shanks  on  drill  steel  of  hammer  drill, 

53. 
Sharpeners  for  drill  steel,   machine, 

157. 
Sharpening  chisel  bits,  156. 

cruciform  bits,  157. 

tools,  272. 

Shaw  machine,  10A,  78. 
Shot  firing,  electric,  204. 

firing,  group  electric,  197. 

weak,  194. 

Siemens-Halske  electric  drill,  86,  89, 
90. 

-Schuckert  electric  drill,  87. 
Signaling    system,    Rand    Collieries, 

Ltd.,  239. 

Simmer  deep,  driving  results,  231. 
Simplex  drill  chuck,  240. 
Sinclair  hammer  drill,  69,  70. 

valveless  hand  drill,  61. 
Siskol  drill,  333. 
"Slugger"  rock  drill,  29. 
Sommeiller  machine,  1,  2. 
South  Africa,  drills  in  use,  226. 

Africa,  rock  drill  practice,  226. 
Spares,  fitted  up,  146. 
Speed,  boring,  332. 

drilling,  332. 
Spitting,  side,  195. 
Sprays,  340. 

Holman,  340. 

Spring,  pawl,  of  hammer  drill,  53. 
Squibbing,  302. 
Standards,  146. 
Starter,  Leyner  patent,  172. 
Starting  steam  drill,  115. 

the  machine,  111. 
Statics  of  fluids  and  gases,  216. 
Steam  drill,  starting,  115. 

in  rock  drill  work,  351. 
Steel,  150. 

drill,  150,  310. 
size  of,  234. 

for  drilling  dry  up-holes,  168. 

hollow  drill,  62,  176,  342. 

sizes,  240. 


Steel    twisted     drill,     for    removing 

broken  rock,  169. 
vanadium,     used    in    hammer    of 

drill,  79. 

Stephens  &  Son,  R.,  65. 
chuck,  48. 
Climax  Imperial  hammer  drill,  65, 

66,  67. 

tappet  valve  drill,  23. 
double  chisel  drill,  176. 
patent  Climax  dust  allay er,  341. 
Sticks,  powder,  diameter  of,  187. 
Stools,  jack,  maintenance,  146. 
Stope-cut,  260,  261. 
drill,  Cleveland,  75. 

competition,  333,  336,  337.  , 

tests,  331. 
-face  showing  run  of  benches,  256. 

with  benches  for  drills,  255. 
ideal  arrangement,  255. 
overhand,  257. 
shape,  252. 
underhand,  257. 

with  benches  at  angle  to  drift,  253. 
pillar  cut  on  lower  side  at  drive, 

253. 

Stoping,  back  versus  underhand,  275. 
Caledonia  mine,  269,  271. 
drift,  307. 

Findley  Consolidated  mine,  285. 
hard  ground,  302. 
Lake  Superior,  295,  298. 
on  the  Witwatersrand,  249. 
overhand,  on  15  to  45  degree  reef, 

252. 

raise,  299. 

underhand,  Davis  mine,  274. 
with  large  machines,  284. 
Wolverine  mine,  292. 
Storage  of  powder,  194. 
Stretcher  bar,  40. 

Sullivan  D-21  air-hammer  drill,  72, 73. 
differential  spool  valve,  29. 

valve  rock  drill,  27,  28. 
drill  on  double-screw   mining  col- 
umn, 41. 

on  single-screw  mining  column, 
41. 


INDEX 


367 


Sullivan  guide  on  cradle,  39. 

hand  hammer  drill,  60. 

rock  drill  bits,  155. 

tappet  valve  rock  drill,  18. 

valve  hand  drill,  61. 
Sump    and    bench    system    of    shaft 

sinking,  244. 
Surface  operation  of  drills,  105. 

Tamping,  220. 

high  explosives,  187. 
Tank  for  Murphy  drill,  339. 
Tappet,  automatic,  Waugh  drill,  76. 

maintenance,  144. 

valve  drills,  12. 
Tempering  drill  bits,  154. 

steel,  150. 
Temple-Ingersoll    electric    air    drill, 

95,  100. 
Tests,  drill,  317,  329,  334. 

electric  and  air  drills,  89,  90. 

horse-power,  325. 

rock  drill,  315,  321,  322,  323,  325, 
330. 

stope  drill,  331. 
Testing  hammer  drills,  147. 
Time,  drilling,  257. 
Tonite,  179. 
Tools,  105. 

blacksmith's,  156. 

sharpening,  272. 

swaging,  for  Kimber  sharpener,  161. 

Torpedo  drill,  30,  31. 

Transvaal   stope   drill,    competition, 

333. 
Tripod  for  mounting  drills,  42. 

working  drill  with,  115. 
Tuckingmill  Foundry  Co.,  Dunstan's 

drill  sharpener,  158. 
Tunnel  driving  speed,  291,  292. 
Tuneling,  first  drill  used,  2. 

rock  drills  in,  291. 

U-bolt  chuck,  45,  48. 
Underground  drilling,  105. 
Utah,  rock  drill  practice,  308. 

Valve,  auxiliary,  31. 

auxiliary,  maintenance,  144. 


Valve  chests,  maintenance,  143. 

design  in  hammer  drill,  81. 

drills,  10. 
auxiliary,  31. 

piston,  maintenance,  143. 

remedy  for  sticking,  116. 

slide,  maintenance,  143. 

spool,  29,  33. 

Sullivan  differential  spool,  29. 

throttle,  maintenance,  143. 
Valveless  drills,  50,  79. 
Van  Dyke  mines,  driving  results,  232. 

Ryn    Gold    Mines    Estate,    Ltd., 

rock  drill  tests,  325. 
Vanadium  in  drill  steel,  177. 
Vibration  of  arm  and  bar,  107. 
Victoria   Reef   Quartz    Mining   Co., 

record  shaft  sinking,  263. 
Vogelstrius  Consolidated  Deep,  driv- 
ing results,  233. 

Wages,  miners',  South  Africa,  256. 
Warren-Tregoning  chuck,  46. 
Water   blast,    variation    of   James's, 

342. 
device   for   passing    through    drill 

steel,  347. 
jets,  338. 

Leyner  hammer  drill,  51,  52. 
.Waugh  drifting  and  stoping  drill,  76, 

77. 

drills,  174,  175. 
Wear  between  cylinder  and  piston, 

142. 

causes,  139. 
effects,  147. 
on  cradle  guides,  142. 
Wedges,  105. 

Weight  of  parts  of  hammer  drill,  139. 
Western  lubricating  valve,  119,  120. 
Witherbee-Sherman  iron  mines,  N.  Y., 

rock  drill  practice,  273. 
Wolverine  bit,  165. 

mine,  rock  drill  practice,  292. 
Word  drill  sharpener,  157,  167. 
Work  done  by  electric  air  drills,  101. 
done   with   multiple   arrangement 
of  drills,  228. 


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SEP    14  1932 


OCT  18  1946 


OCT  0  5 


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INTERLfBRARY  LOAN 

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